On Wed, 31 Aug 2022 at 14:30, Patrick Palka <ppa...@redhat.com> wrote:
>
> On Wed, 31 Aug 2022, Jonathan Wakely wrote:
>
> > On Tue, 30 Aug 2022 at 18:14, Patrick Palka via Libstdc++
> > <libstd...@gcc.gnu.org> wrote:
> > >
> > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> >
> >
> > > + constexpr
> > > + _Iterator(__as_sentinel, iterator_t<_Base> __first,
> > > iterator_t<_Base> __last)
> > > + {
> > > + if constexpr (!bidirectional_range<_Base>)
> > > + for (auto& __it : _M_current)
> > > + __it = __last;
> > > + else
> > > + for (ssize_t __i = _Nm-1; __i >= 0; --__i)
> >
> > ssize_t is defined by POSIX in <sys/types.h> but isn't in ISO C or
> > C++. It looks like MinGW defines it to ... something ... sometimes,
> > but I don't think we can rely on it for non-POSIX targets.
>
> I see. Using ssize_t makes the loop a little cleaner but it's hardly
> necessary, so consider it rewritten into:
>
> for (size_t __i = 0; __i < _Nm; ++__i)
> {
> _M_current[_Nm - 1 - __i] = __last;
> ranges::advance(__last, -1, __first);
> }
>
> >
> >
> > > + template<size_t _Nm>
> > > + struct _Adjacent : __adaptor::_RangeAdaptorClosure
> > > + {
> > > + template<viewable_range _Range>
> > > + requires (_Nm == 0) || __detail::__can_adjacent_view<_Nm,
> > > _Range>
> > > + [[nodiscard]]
> > > + constexpr auto
> > > + operator()(_Range&& __r) const
> >
> > Does this attribute actually work here?
> >
> > I thought we needed to use `operator() [[nodiscard]]` for functions
> > with a requires-clause, because otherwise the attribute gives a parse
> > error. Maybe I've misremembered the problem, and it just doesn't give
> > a -Wunused-result warning. The decl above is setting off my spidey
> > sense for some reason though.
>
> Oops yeah, it looks like this position of [[nodiscard]] works with
> standard concepts, but it's a parse error with -fconcepts-ts due to the
> different requires-clause grammar.
>
> Here's v2 which avoids using ssize_t, and puts the [[nodiscard]] after
> 'operator()' (_Zip and _ZipTransform have the same issue which I can
> fix separately):
OK for trunk with those changes, thanks.
