[PATCH] libstdc++: Avoid hard error in ranges::unique_copy [PR100770]

[Tim Song]

On Wed, May 26, 2021 at 1:43 PM Patrick Palka <ppalka@redhat.com> wrote:
>
> On Wed, 26 May 2021, Tim Song wrote:
> >
> > On Wed, May 26, 2021 at 12:00 PM Patrick Palka via Libstdc++
> > <libstdc++@gcc.gnu.org> wrote:
> > >
> > > -       else if constexpr (input_iterator<_Out>
> > > -                          && same_as<iter_value_t<_Iter>, iter_value_t<_Out>>)
> > > +       else if constexpr (requires { requires (input_iterator<_Out>
> > > +                                               && same_as<iter_value_t<_Iter>,
> > > +                                                          iter_value_t<_Out>>); })
> >
> > It's arguably cleaner to extract this into a concept which can then
> > also be used in the constraint.
>
> Sounds good, though I'm not sure what name to give to this relatively
> ad-hoc set of requirements.  Any suggestions? :)
>

Something along the lines of "__can_reread_output", perhaps?