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Re: [PATCH] Add std::string constructor for substring of string_view (LWG 2742)
- From: Jonathan Wakely <jwakely at redhat dot com>
- To: libstdc++ at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Tue, 15 Nov 2016 19:32:46 +0000
- Subject: Re: [PATCH] Add std::string constructor for substring of string_view (LWG 2742)
- Authentication-results: sourceware.org; auth=none
- References: <20161115143349.GG3145@redhat.com>
On 15/11/16 14:33 +0000, Jonathan Wakely wrote:
This is another issue resolution for C++17 features that was approved
at the recent meeting. I think this resolution is wrong too, but in
this case the fix is obvious so I've gone ahead and done it.
* doc/xml/manual/intro.xml: Document LWG 2742 status.
* doc/html/*: Regenerate.
* include/bits/basic_string.h
(basic_string(const T&, size_type, size_type, const Allocator&)): Add
constructor for substring of basic_string_view, as per LWG 2742 but
with additional constraint to fix ambiguity.
* testsuite/21_strings/basic_string/cons/char/9.cc: New test.
* testsuite/21_strings/basic_string/cons/wchar_t/9.cc: New test.
Tested powerpc64le-linux, comitted to trunk.
I forgot I already added an convenience alias template for checking
the condition in this patch.
Tested powerpc64le-linux, comitted to trunk.
commit f7852de7c77f0d9cc8520d10549da0652e334dc7
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Nov 15 18:55:35 2016 +0000
Use existing helper for new std::string constructor
* include/bits/basic_string.h: Reuse _If_sv alias template for new
constructor.
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 943e88d..9af7bfb 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -585,6 +585,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
{ _M_construct(__beg, __end); }
#if __cplusplus > 201402L
+ template<typename _Tp, typename _Res>
+ using _If_sv = enable_if_t<
+ __and_<is_convertible<const _Tp&, __sv_type>,
+ __not_<is_convertible<const _Tp&, const _CharT*>>>::value,
+ _Res>;
+
/**
* @brief Construct string from a substring of a string_view.
* @param __t Source string view.
@@ -592,9 +598,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* @param __n The number of characters to copy from __t.
* @param __a Allocator to use.
*/
- template<typename _Tp, typename =
- _Require<is_convertible<_Tp, __sv_type>,
- __not_<is_convertible<const _Tp&, const _CharT*>>>>
+ template<typename _Tp, typename = _If_sv<_Tp, void>>
basic_string(const _Tp& __t, size_type __pos, size_type __n,
const _Alloc& __a = _Alloc())
: basic_string(__sv_type(__t).substr(__pos, __n), __a) { }
@@ -1252,12 +1256,6 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
append(__sv_type __sv)
{ return this->append(__sv.data(), __sv.size()); }
- template<typename _Tp, typename _Res>
- using _If_sv = enable_if_t<
- __and_<is_convertible<const _Tp&, __sv_type>,
- __not_<is_convertible<const _Tp&, const _CharT*>>>::value,
- _Res>;
-
/**
* @brief Append a range of characters from a string_view.
* @param __sv The string_view to be appended from.