[libstdc++-v3] PR 59529, 59530, 59531 Was(Re: Implement N3762 string_view: a non-owning reference to a string.)

[Ed Smith-Rowland <3dw4rd at verizon dot net>]

On 12/17/2013 11:06 AM, Peter A. Bigot wrote:
> On 11/20/2013 08:09 AM, Ed Smith-Rowland wrote:
> > On 11/18/2013 09:08 AM, Daniel Krügler wrote:
> > > 2013/11/15 Ed Smith-Rowland <3dw4rd@verizon.net>:
> > > > Greetings,
> > > >
> > > > As the title says.  It's a pretty simple class" a non-mutating 
> > > > read-only
> > > > view into a const CharT* or a basic_string.
> > > >
> > > > Built and tested on x86_64-linux.
> > > >
> > > > OK?
> > > Sorry, if this is documented somewhere, but is this intended to 
> > > implement
> > >
> > > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3762.html
> > >
> > > ? I don't think that your implementation is valid, because it maps an
> > > empty string view into a NULL data pointer. But according to the
> > > specification of data() the return type, this isn't feasible:
> > >
> > > <quote>
> > > constexpr const charT* data() const noexcept;
> > >
> > > Returns: A non-null pointer p such that p + i == &operator[](i) for
> > > each i in [0,size()).
> > > </quote>
> > >
> > > - Daniel
> > Right.
> >
> > Here is a fix that introduces an constexpr unit length string to
> > represent empty strings so that refs to empty strings don't point to the
> > ether.
>
> Thanks for providing this feature; I'm finding it very useful.
>
> There's a small problem with this fix in that some zero-length
> string_views should remain pointing into the referenced object, and not
> be remapped to the constexpr one. This showed up after fixing a boundary
> condition problem with substr, recorded in:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59529
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59530 notes a similar
> problem with operator[], and
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59531 fixes a buffer overrun
> in copy().  Proposed patches are attached to each issue.
>
> Peter

I've looked over these patches (thanks Peter!) and tweaked up a couple 
patches (no need to leave commented out tests, and copy can start from 
pos=length()).
I'm finishing testing on x86_64-linux.

Paolo, are there any Copyright issues we need to be aware of?  Does 
Peter need a Copyright form?  These are fairly obvious one-liners I 
think.  There are no real alternatives to these patches.  What ChangeLog 
attribution is appropriate?

Ed

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