On Mon, 14 Nov 2022 at 10:17, Daniel Krügler <daniel.krueg...@gmail.com> wrote:
>
> Am Mo., 14. Nov. 2022 um 11:09 Uhr schrieb Jonathan Wakely via
> Libstdc++ <libstd...@gcc.gnu.org>:
> >
> > On Mon, 14 Nov 2022 at 04:52, Patrick Palka via Libstdc++
> > <libstd...@gcc.gnu.org> wrote:
> > >
> > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> > >
> > > libstdc++-v3/ChangeLog:
> > >
> > > * include/bits/ranges_algo.h (out_value_result): Define.
> > > (iota_result): Define.
> > > (__iota_fn, iota): Define.
> > > * testsuite/25_algorithms/iota/1.cc: New test.
> > > ---
> > > libstdc++-v3/include/bits/ranges_algo.h | 48 +++++++++++++++++++
> > > .../testsuite/25_algorithms/iota/1.cc | 29 +++++++++++
> > > 2 files changed, 77 insertions(+)
> > > create mode 100644 libstdc++-v3/testsuite/25_algorithms/iota/1.cc
> > >
> > > diff --git a/libstdc++-v3/include/bits/ranges_algo.h
> > > b/libstdc++-v3/include/bits/ranges_algo.h
> > > index da0ca981dc3..f003117c569 100644
> > > --- a/libstdc++-v3/include/bits/ranges_algo.h
> > > +++ b/libstdc++-v3/include/bits/ranges_algo.h
> > > @@ -3517,6 +3517,54 @@ namespace ranges
> > > };
> > >
> > > inline constexpr __contains_subrange_fn contains_subrange{};
> > > +
> > > + template<typename _Out, typename _Tp>
> > > + struct out_value_result
> > > + {
> > > + [[no_unique_address]] _Out out;
> > > + [[no_unique_address]] _Tp value;
> > > +
> > > + template<typename _Out2, typename _Tp2>
> > > + requires convertible_to<const _Out&, _Out2>
> > > + && convertible_to<const _Tp&, _Tp2>
> > > + constexpr
> > > + operator out_value_result<_Out2, _Tp2>() const &
> > > + { return {out, value}; }
> > > +
> > > + template<typename _Out2, typename _Tp2>
> > > + requires convertible_to<_Out, _Out2>
> > > + && convertible_to<_Tp, _Tp2>
> > > + constexpr
> > > + operator out_value_result<_Out2, _Tp2>() &&
> > > + { return {std::move(out), std::move(value)}; }
> > > + };
> > > +
> > > + template<typename _Out, typename _Tp>
> > > + using iota_result = out_value_result<_Out, _Tp>;
> > > +
> > > + struct __iota_fn
> > > + {
> > > + template<input_or_output_iterator _Out, sentinel_for<_Out> _Sent,
> > > weakly_incrementable _Tp>
> > > + requires indirectly_writable<_Out, const _Tp&>
> > > + constexpr iota_result<_Out, _Tp>
> > > + operator()(_Out __first, _Sent __last, _Tp __value) const
> > > + {
> > > + while (__first != __last)
> > > + {
> > > + *__first = static_cast<add_const_t<_Tp>&>(__value);
> >
> > Is this any different to const_cast<const _Tp&>(__value) ?
>
> I think it is. const_cast<const _Tp&> can potentially mean the removal
> of volatile,
True.
> so I would always look with suspicion on const_cast<const
> _Tp&>, while static_cast is clearer. Alternatively, as_const could be
> used, which does add_const_t.
Which means evaluating the add_const trait *and* overload resolution
for as_const* *and* a runtime function call.
Let's go with static_cast<const _Tp&>.
