[PATCH v1] libstdc++: Fix class mandate for extents.

[Tomasz Kaminski]

No strong preference, but Ville's argument sounds reasonable.

On Thu, May 15, 2025 at 12:25 PM Ville Voutilainen <
ville.voutilainen@gmail.com> wrote:

> Mild preference against; use the names from the standard, not the
> implementation, in such diagnostics.
>
> to 15. toukok. 2025 klo 13.20 Jonathan Wakely <jwakely@redhat.com>
> kirjoitti:
>
>> On Thu, 15 May 2025 at 11:14, Jonathan Wakely <jwakely@redhat.com> wrote:
>> >
>> > On Wed, 14 May 2025 at 20:18, Luc Grosheintz <luc.grosheintz@gmail.com>
>> wrote:
>> > >
>> > > The standard states that the IndexType must be a signed or unsigned
>> > > integer. This mandate was implemented using `std::is_integral_v`.
>> Which
>> > > also includes (among others) char and bool, which neither signed nor
>> > > unsigned integers.
>> > >
>> > > libstdc++-v3/ChangeLog:
>> > >
>> > >         * include/std/mdspan: Implement the mandate for extents as
>> > >         signed or unsigned integer and not any interal type.
>> > >         *
>> testsuite/23_containers/mdspan/extents/class_mandates_neg.cc: Check
>> > >         that extents<char,...> and extents<bool,...> are invalid.
>> > >         * testsuite/23_containers/mdspan/extents/misc.cc: Update
>> > >         tests to avoid `char` and `bool` as IndexType.
>> > > ---
>> > >  libstdc++-v3/include/std/mdspan                        |  3 ++-
>> > >  .../23_containers/mdspan/extents/class_mandates_neg.cc | 10
>> +++++++---
>> > >  .../testsuite/23_containers/mdspan/extents/misc.cc     |  8 ++++----
>> > >  3 files changed, 13 insertions(+), 8 deletions(-)
>> > >
>> > > diff --git a/libstdc++-v3/include/std/mdspan
>> b/libstdc++-v3/include/std/mdspan
>> > > index aee96dda7cd..22509d9c8f4 100644
>> > > --- a/libstdc++-v3/include/std/mdspan
>> > > +++ b/libstdc++-v3/include/std/mdspan
>> > > @@ -163,7 +163,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> > >    template<typename _IndexType, size_t... _Extents>
>> > >      class extents
>> > >      {
>> > > -      static_assert(is_integral_v<_IndexType>, "_IndexType must be
>> integral.");
>> > > +      static_assert(__is_standard_integer<_IndexType>::value,
>> > > +                   "_IndexType must be a signed or unsigned
>> integer.");
>> >
>> > GCC's diagnostics never end with a full stop (aka period), and we
>> > follow that convention for our static assertions.
>> >
>> > So I'll remove the '.' at the end of the string literal, and then push
>> > this to trunk.
>> >
>> >
>> > >        static_assert(
>> > >           (__mdspan::__valid_static_extent<_Extents, _IndexType> &&
>> ...),
>> > >           "Extents must either be dynamic or representable as
>> _IndexType");
>>
>> I've just noticed that this static_assert refers to "Extents" without
>> the leading underscore, but "_IndexType" with a leading underscore.
>>
>> I think it's OK to omit the leading underscore, it might be a bit more
>> user-friendly and I don't think anybody will be confused by the fact
>> it's not identical to the real template parameter. But we should
>> either do it consistently for _Extents and _IndexType or for neither
>> of them.
>>
>> Anybody want to argue for or against underscores?
>>
>>
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