On Mon, 14 Nov 2022, Jonathan Wakely wrote:
> 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&>.
Sounds good, like so?
-- >8 --
Subject: [PATCH 2/3] libstdc++: Implement ranges::iota from P2440R1
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 11206bdbcaa..f75735f02cb 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<const _Tp&>(__value);
+ ++__first;
+ ++__value;
+ }
+ return {std::move(__first), std::move(__value)};
+ }
+
+ template<weakly_incrementable _Tp, output_range<const _Tp&> _Range>
+ constexpr iota_result<borrowed_iterator_t<_Range>, _Tp>
+ operator()(_Range&& __r, _Tp __value) const
+ { return (*this)(ranges::begin(__r), ranges::end(__r),
std::move(__value)); }
+ };
+
+ inline constexpr __iota_fn iota{};
#endif // C++23
} // namespace ranges
diff --git a/libstdc++-v3/testsuite/25_algorithms/iota/1.cc
b/libstdc++-v3/testsuite/25_algorithms/iota/1.cc
new file mode 100644
index 00000000000..ad2bf08adf5
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/iota/1.cc
@@ -0,0 +1,29 @@
+// { dg-options "-std=gnu++23" }
+// { dg-do run { target c++23 } }
+
+#include <algorithm>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+namespace ranges = std::ranges;
+
+void
+test01()
+{
+ int x[3] = {};
+ __gnu_test::test_output_range<int> rx(x);
+ auto r0 = ranges::iota(rx, 0);
+ VERIFY( r0.out.ptr == x+3 );
+ VERIFY( r0.value == 3 );
+ VERIFY( ranges::equal(x, (int[]){0,1,2}) );
+ auto r1 = ranges::iota(x, x+2, 5);
+ VERIFY( r1.out == x+2 );
+ VERIFY( r1.value == 7 );
+ VERIFY( ranges::equal(x, (int[]){5,6,2}) );
+}
+
+int
+main()
+{
+ test01();
+}
--
2.38.1.420.g319605f8f0
