[PATCH] libstdc++: Implement P3060R3: Add std::views::indices(n)

[Yuao Ma]

Hi Jonathan,

Thanks for the information about the standard wording. Regarding this
patch, I'm wondering does it need any further refinement?

Yuao

On Wed, Oct 15, 2025 at 12:32 AM Yuao Ma <addr2line@gmail.com> wrote:
>
> On Wed, Oct 15, 2025 at 12:21 AM Jonathan Wakely <jwakely@redhat.com> wrote:
> >
> > On Tue, 14 Oct 2025 at 17:08, Yuao Ma <addr2line@gmail.com> wrote:
> > >
> > > Hi Hewill and Jonathan,
> > >
> > > On Tue, Oct 14, 2025 at 11:39 PM Hewill Kang <hewillk@gmail.com> wrote:
> > > >
> > > > 1. The prefix ranges:: in ranges::__detail::__is_integer_like can be removed.
> > >
> > > It can't. views has its own __detail namespace.
> > >
> > > > 2. Parameters should not be passed by reference; otherwise, const int i = 0; std::views::indices(i); will fail because const int& does not satisfy __is_integer_like.
> > >
> > > Yes I figure that out with the new testcase. Done.
> > >
> > > > 3. operator() can be static.
> > >
> > > I think I'll stick to the style of the existing functions.
> >
> > static operator() is a C++23 feature, so wasn't an option for the
> > original C++20 views.
> >
> > I'm not sure it makes much difference on the ABI used for most of our
> > supported targets, and it should be optimized away anyway. In fact, we
> > could add [[__gnu__::__always_inline__]] to the operator() here, since
> > it's incredibly simple.
> >
> >
> > > The testcase got updated, testing against different type and size. But
> > > ranges::__detail::max_{size, diff}_type not working here:
> >
> > Ah yes, that's a problem. If you create
> > views::indices(ranges::distance(views::iota(0ULL, 1ULL))) then you
> > need to create an iota_view of the difference type of iota(0ULL,
> > 1ULL), but that can't be represented. You would need an integer-like
> > type wider than our widest integer-like type.
> >
> > That might be a defect in the wording for views::indices, but that's
> > not your concern. There's no need to test it with that type then.
> >
>
> The updated patch is rfr now. Testcase updated with noexcept check.
>
> Yuao