[PATCH] libstdc++: Implement P2408R5 Ranges iterators as inputs to non-Ranges algorithms
Tomasz Kaminski
tkaminsk@redhat.com
Tue Nov 25 14:15:00 GMT 2025
On Tue, Nov 25, 2025 at 3:07 PM Patrick Palka <ppalka@redhat.com> wrote:
> On Tue, 25 Nov 2025, Tomasz Kaminski wrote:
>
> >
> >
> > On Tue, Nov 25, 2025 at 2:58 PM Patrick Palka <ppalka@redhat.com> wrote:
> > On Tue, 25 Nov 2025, Tomasz Kaminski wrote:
> >
> > >
> > >
> > > On Tue, Nov 25, 2025 at 2:28 PM Patrick Palka <ppalka@redhat.com>
> wrote:
> > > changes in v4: define the new helpers in
> stl_iterator_base_funcs.h
> > > rather than stl_iterator_base_types.h. also define an
> __iter_move_val
> > > helper
> > >
> > > changes v3: add inclusive_scan test using zip's proxy
> iterator. rename
> > > tests from p2408r5.cc to c++20_iter.cc
> > >
> > > changes v2: more tests, and the one-argument version of
> > > __iter_concept_or_category is now constexpr instead of
> > > consteval
> > >
> > > -- >8 --
> > >
> > > From the paper's abstract:
> > >
> > > Change the iterator requirements for non-Ranges
> algorithms. For
> > > forward iterators and above that are constant iterators,
> instead of
> > > requiring that iterators meet certain Cpp17...Iterator
> requirements,
> > > require that the iterators model certain iterator
> concepts. This makes
> > > iterators from several standard views usable with
> non-Ranges
> > > algorithms that require forward iterators or above, such
> as the
> > > parallel overloads of most algorithms.
> > >
> > > This patch narrowly implements P2408R5 in C++23 mode and
> C++20 mode
> > > (as an extension). "Narrowly" because just as in the
> paper, we don't
> > > attempt to relax the requirements of mutable iterators
> even though it's
> > > possible in theory. Note that the PSTL algorithm
> requirements have
> > > already been relaxed in r15-3650. And we don't bother
> touching the
> > > deprecated parallel mode algorithms under include/parallel.
> > >
> > > The main workhorse of this paper is a new helper
> > > __iterator_concept_or_category that replaces existing uses
> of
> > > __iterator_category and iterator_traits::iterator_category
> with constant
> > > iterators. This new helper considers both the
> iterator_concept and
> > > iterator_category of the given iterator and returns the
> former if it's
> > > at least as strong as the latter. It's implemented in
> terms of the
> > > __promotable_iterator concept added in r16-2588 that made
> std::advance
> > > etc aware of C++20 iterators. Note that this helper
> doesn't check the
> > > actual C++20 iterator concepts (which check syntactic
> requirements along
> > > with iterator_concept if it's defined) and instead just
> checks for, and
> > > fully trusts, the iterator_concept defined by the iterator
> type. This
> > > is a slight deviation from the paper but IMHO it's
> consistent with the
> > > existing trusting of iterator_category and should be good
> enough in
> > > practice, though it means C++20 iterators that don't define
> > > iterator_concept will not be recognized as such by this
> helper even if
> > > they otherwise model the std::foo_iterator concept. (An
> undefined
> > > iterator_concept effectively defaults to
> random_access_iterator_tag.)
> > >
> > > Most of the changes made here are effectively
> optimizations that don't
> > > have a semantic impact, e.g. for std::reduce. I added
> tests for a
> > > couple of algorithms where these changes are observable.
> > >
> > > The new __iterator_concept_or_category helper can probably
> also be used
> > > to fix PR100070 "Standard library container iterator-pair
> constructors
> > > should check C++20 iterator concepts".
> > >
> > > As a follow-up to this patch we should either remove the
> Boost-style
> > > concept checks, or relax them accordingly. It seems we're
> leaning
> > > towards removing them outright; see this thread:
> > >
> https://gcc.gnu.org/pipermail/libstdc++/2025-May/061568.html
> > >
> > > As suggested by Tomasz, this patch also introduces an
> __iter_move_val
> > > wrapper around ranges::iter_move that also converts to the
> iterator's
> > > value type and is usable before C++20 as well.
> > >
> > > PR libstdc++/113299
> > >
> > > libstdc++-v3/ChangeLog:
> > >
> > > * include/bits/deque.tcc (__copy_move_a1):
> Constrain with
> > > __is_any_random_access_iter instead of
> __is_random_access_iter.
> > > (__copy_move_backward_a1): Likewise.
> > > (__equal_aux1): Likewise.
> > > * include/bits/stl_algo.h (__search_n): Use
> > > __iter_concept_or_category instead of
> __iterator_category
> > > or iterator_traits::iterator_category.
> > > (find_end): Likewise.
> > > (__is_permutation): Likewise.
> > > (for_each_n): Likewise.
> > > (unique_copy): Likewise, for constant iterators.
> > > (sample): Likewise, for constant iterators.
> > > * include/bits/stl_algobase.h (__copy_move_a1):
> Adjust
> > > deque-based forward declaration accordingly.
> > > (__copy_move_backward_a1): Likewise.
> > > (__equal_aux1): Likewise.
> > > (__lexicographical_compare_impl): Use
> > > __iter_concept_or_category instead of
> __iterator_category or
> > > iterator_traits::iterator_category.
> > > (__equal4): Likewise.
> > > * include/bits/stl_iterator_base_funcs.h
> > > (__iter_concept_or_category): New.
> > > (__is_any_random_access_iter): New.
> > > (__iter_move_val): New.
> > > * include/bits/stl_uninitialized.h
> (uninitialized_copy_n):
> > > Use __iterator_concept_or_category instead of
> > > __iterator_category for the constant iterator
> __first.
> > > (__uninitialized_copy_n_pair): Likewise.
> > > * include/bits/version.def
> (algorithm_iterator_requirements):
> > > Define.
> > > * include/bits/version.h: Regenerate.
> > > * include/std/algorithm: Provide the FTM
> > > __cpp_lib_algorithm_iterator_requirements.
> > > * include/std/memory: Likewise.
> > > * include/std/numeric: Likewise.
> > > (reduce): Use __is_any_random_access_iter instead
> of
> > > __is_random_access_iter.
> > > (transform_reduce): Likewise.
> > > (inclusive_scan): Use __iter_move_val instead of
> std::move.
> > > * testsuite/25_algorithms/find_end/c++20_iter.cc:
> New test.
> > > * testsuite/25_algorithms/sample/c++20_iter.cc:
> New test.
> > > * testsuite/25_algorithms/search_n/c++20_iter.cc:
> New test.
> > > *
> testsuite/25_algorithms/unique_copy/c++20_iter.cc: New test.
> > > *
> testsuite/26_numerics/inclusive_scan/c++20_iter.cc: New test.
> > > ---
> > > libstdc++-v3/include/bits/deque.tcc | 8 +--
> > > libstdc++-v3/include/bits/stl_algo.h | 28
> ++++----
> > > libstdc++-v3/include/bits/stl_algobase.h | 20 +++---
> > > .../include/bits/stl_iterator_base_funcs.h | 70
> +++++++++++++++++++
> > > libstdc++-v3/include/bits/stl_uninitialized.h | 4 +-
> > > libstdc++-v3/include/bits/version.def | 9 +++
> > > libstdc++-v3/include/bits/version.h | 10 +++
> > > libstdc++-v3/include/std/algorithm | 1 +
> > > libstdc++-v3/include/std/memory | 1 +
> > > libstdc++-v3/include/std/numeric | 11 +--
> > > .../25_algorithms/find_end/c++20_iter.cc | 23 ++++++
> > > .../25_algorithms/sample/c++20_iter.cc | 23 ++++++
> > > .../25_algorithms/search_n/c++20_iter.cc | 21 ++++++
> > > .../25_algorithms/unique_copy/c++20_iter.cc | 33
> +++++++++
> > > .../26_numerics/inclusive_scan/c++20_iter.cc | 26 +++++++
> > > 15 files changed, 253 insertions(+), 35 deletions(-)
> > > create mode 100644
> libstdc++-v3/testsuite/25_algorithms/find_end/c++20_iter.cc
> > > create mode 100644
> libstdc++-v3/testsuite/25_algorithms/sample/c++20_iter.cc
> > > create mode 100644
> libstdc++-v3/testsuite/25_algorithms/search_n/c++20_iter.cc
> > > create mode 100644
> libstdc++-v3/testsuite/25_algorithms/unique_copy/c++20_iter.cc
> > > create mode 100644
> libstdc++-v3/testsuite/26_numerics/inclusive_scan/c++20_iter.cc
> > >
> > > diff --git a/libstdc++-v3/include/bits/deque.tcc
> b/libstdc++-v3/include/bits/deque.tcc
> > > index 20b23fffc9e1..e409f3a3fc57 100644
> > > --- a/libstdc++-v3/include/bits/deque.tcc
> > > +++ b/libstdc++-v3/include/bits/deque.tcc
> > > @@ -1225,7 +1225,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > >
> > > template<bool _IsMove, typename _II, typename _Tp>
> > > typename __gnu_cxx::__enable_if<
> > > - __is_random_access_iter<_II>::__value,
> > > + __is_any_random_access_iter<_II>::__value,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*>
> >::__type
> > > __copy_move_a1(_II __first, _II __last,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp,
> _Tp&, _Tp*> __result)
> > > @@ -1347,7 +1347,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > >
> > > template<bool _IsMove, typename _II, typename _Tp>
> > > typename __gnu_cxx::__enable_if<
> > > - __is_random_access_iter<_II>::__value,
> > > + __is_any_random_access_iter<_II>::__value,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*>
> >::__type
> > > __copy_move_backward_a1(_II __first, _II __last,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&,
> _Tp*> __result)
> > > @@ -1406,7 +1406,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > >
> > > template<typename _Tp, typename _Ref, typename _Ptr,
> typename _II>
> > > typename __gnu_cxx::__enable_if<
> > > - __is_random_access_iter<_II>::__value, bool>::__type
> > > + __is_any_random_access_iter<_II>::__value,
> bool>::__type
> > > __equal_aux1(_GLIBCXX_STD_C::_Deque_iterator<_Tp,
> _Ref, _Ptr> __first1,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp,
> _Ref, _Ptr> __last1,
> > > _II __first2)
> > > @@ -1422,7 +1422,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > >
> > > template<typename _II, typename _Tp, typename _Ref,
> typename _Ptr>
> > > typename __gnu_cxx::__enable_if<
> > > - __is_random_access_iter<_II>::__value, bool>::__type
> > > + __is_any_random_access_iter<_II>::__value,
> bool>::__type
> > > __equal_aux1(_II __first1, _II __last1,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Ref,
> _Ptr> __first2)
> > > {
> > > diff --git a/libstdc++-v3/include/bits/stl_algo.h
> b/libstdc++-v3/include/bits/stl_algo.h
> > > index bbd1800af779..0d8f7af9d272 100644
> > > --- a/libstdc++-v3/include/bits/stl_algo.h
> > > +++ b/libstdc++-v3/include/bits/stl_algo.h
> > > @@ -226,7 +226,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > > return std::__find_if(__first, __last,
> __unary_pred);
> > >
> > > return std::__search_n_aux(__first, __last,
> __count, __unary_pred,
> > > -
> std::__iterator_category(__first));
> > > +
> std::__iter_concept_or_category(__first));
> > > }
> > >
> > > // find_end for forward iterators.
> > > @@ -337,8 +337,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > > __glibcxx_requires_valid_range(__first2, __last2);
> > >
> > > return std::__find_end(__first1, __last1, __first2,
> __last2,
> > > -
> std::__iterator_category(__first1),
> > > -
> std::__iterator_category(__first2),
> > > +
> std::__iter_concept_or_category(__first1),
> > > +
> std::__iter_concept_or_category(__first2),
> > > __gnu_cxx::__ops::equal_to());
> > > }
> > >
> > > @@ -388,8 +388,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > > __glibcxx_requires_valid_range(__first2, __last2);
> > >
> > > return std::__find_end(__first1, __last1, __first2,
> __last2,
> > > -
> std::__iterator_category(__first1),
> > > -
> std::__iterator_category(__first2),
> > > +
> std::__iter_concept_or_category(__first1),
> > > +
> std::__iter_concept_or_category(__first2),
> > > __comp);
> > > }
> > >
> > > @@ -3495,9 +3495,9 @@
> _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > > _BinaryPredicate __pred)
> > > {
> > > using _Cat1
> > > - = typename
> iterator_traits<_ForwardIterator1>::iterator_category;
> > > + =
> __decltype(std::__iter_concept_or_category<_ForwardIterator1>());
> > > using _Cat2
> > > - = typename
> iterator_traits<_ForwardIterator2>::iterator_category;
> > > + =
> __decltype(std::__iter_concept_or_category<_ForwardIterator2>());
> > > using _It1_is_RA = is_same<_Cat1,
> random_access_iterator_tag>;
> > > using _It2_is_RA = is_same<_Cat2,
> random_access_iterator_tag>;
> > > constexpr bool __ra_iters = __and_<_It1_is_RA,
> _It2_is_RA>::value;
> > > @@ -3800,7 +3800,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > > for_each_n(_InputIterator __first, _Size __n,
> _Function __f)
> > > {
> > > auto __n2 = std::__size_to_integer(__n);
> > > - using _Cat = typename
> iterator_traits<_InputIterator>::iterator_category;
> > > + using _Cat =
> __decltype(std::__iter_concept_or_category<_InputIterator>());
> > > if constexpr
> (is_base_of_v<random_access_iterator_tag, _Cat>)
> > > {
> > > if (__n2 <= 0)
> > > @@ -4450,7 +4450,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > > return __result;
> > > return std::__unique_copy(__first, __last, __result,
> > >
> __gnu_cxx::__ops::equal_to(),
> > > -
> std::__iterator_category(__first));
> > > +
> std::__iter_concept_or_category(__first));
> > > }
> > >
> > > /**
> > > @@ -4491,7 +4491,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > > if (__first == __last)
> > > return __result;
> > > return std::__unique_copy(__first, __last,
> __result, __binary_pred,
> > > -
> std::__iterator_category(__first));
> > > +
> std::__iter_concept_or_category(__first));
> > > }
> > >
> > > #if __cplusplus <= 201103L || _GLIBCXX_USE_DEPRECATED
> > > @@ -5881,10 +5881,10 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > > _SampleIterator __out, _Distance __n,
> > > _UniformRandomBitGenerator&& __g)
> > > {
> > > - using __pop_cat = typename
> > > -
> std::iterator_traits<_PopulationIterator>::iterator_category;
> > > - using __samp_cat = typename
> > > -
> std::iterator_traits<_SampleIterator>::iterator_category;
> > > + using __pop_cat
> > > + =
> __decltype(std::__iter_concept_or_category<_PopulationIterator>());
> > > + using __samp_cat
> > > + = typename
> iterator_traits<_SampleIterator>::iterator_category;
> > >
> > > static_assert(
> > > __or_<is_convertible<__pop_cat,
> forward_iterator_tag>,
> > > diff --git a/libstdc++-v3/include/bits/stl_algobase.h
> b/libstdc++-v3/include/bits/stl_algobase.h
> > > index 443cbef76dee..701910afd837 100644
> > > --- a/libstdc++-v3/include/bits/stl_algobase.h
> > > +++ b/libstdc++-v3/include/bits/stl_algobase.h
> > > @@ -480,7 +480,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > >
> > > template<bool _IsMove, typename _II, typename _Tp>
> > > typename __gnu_cxx::__enable_if<
> > > - __is_random_access_iter<_II>::__value,
> > > + __is_any_random_access_iter<_II>::__value,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*>
> >::__type
> > > __copy_move_a1(_II, _II,
> _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*>);
> > >
> > > @@ -769,7 +769,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > >
> > > template<bool _IsMove, typename _II, typename _Tp>
> > > typename __gnu_cxx::__enable_if<
> > > - __is_random_access_iter<_II>::__value,
> > > + __is_any_random_access_iter<_II>::__value,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*>
> >::__type
> > > __copy_move_backward_a1(_II, _II,
> > >
> _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*>);
> > > @@ -1219,7 +1219,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > >
> > > template<typename _Tp, typename _Ref, typename _Ptr,
> typename _II>
> > > typename __gnu_cxx::__enable_if<
> > > - __is_random_access_iter<_II>::__value, bool>::__type
> > > + __is_any_random_access_iter<_II>::__value,
> bool>::__type
> > > __equal_aux1(_GLIBCXX_STD_C::_Deque_iterator<_Tp,
> _Ref, _Ptr>,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp,
> _Ref, _Ptr>,
> > > _II);
> > > @@ -1233,7 +1233,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > >
> > > template<typename _II, typename _Tp, typename _Ref,
> typename _Ptr>
> > > typename __gnu_cxx::__enable_if<
> > > - __is_random_access_iter<_II>::__value, bool>::__type
> > > + __is_any_random_access_iter<_II>::__value,
> bool>::__type
> > > __equal_aux1(_II, _II,
> > > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Ref,
> _Ptr>);
> > >
> > > @@ -1332,8 +1332,8 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > > _II2 __first2, _II2
> __last2,
> > > _Compare __comp)
> > > {
> > > - typedef typename
> iterator_traits<_II1>::iterator_category _Category1;
> > > - typedef typename
> iterator_traits<_II2>::iterator_category _Category2;
> > > + typedef
> __decltype(std::__iter_concept_or_category<_II1>()) _Category1;
> > > + typedef
> __decltype(std::__iter_concept_or_category<_II2>()) _Category2;
> > > typedef std::__lc_rai<_Category1, _Category2>
> __rai_type;
> > >
> > > __last1 = __rai_type::__newlast1(__first1, __last1,
> __first2, __last2);
> > > @@ -1649,8 +1649,8 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > > __equal4(_II1 __first1, _II1 __last1, _II2 __first2,
> _II2 __last2)
> > > {
> > > using _RATag = random_access_iterator_tag;
> > > - using _Cat1 = typename
> iterator_traits<_II1>::iterator_category;
> > > - using _Cat2 = typename
> iterator_traits<_II2>::iterator_category;
> > > + using _Cat1 =
> __decltype(std::__iter_concept_or_category<_II1>());
> > > + using _Cat2 =
> __decltype(std::__iter_concept_or_category<_II2>());
> > > using _RAIters = __and_<is_same<_Cat1, _RATag>,
> is_same<_Cat2, _RATag>>;
> > > if constexpr (_RAIters::value)
> > > {
> > > @@ -1676,8 +1676,8 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > > _BinaryPredicate __binary_pred)
> > > {
> > > using _RATag = random_access_iterator_tag;
> > > - using _Cat1 = typename
> iterator_traits<_II1>::iterator_category;
> > > - using _Cat2 = typename
> iterator_traits<_II2>::iterator_category;
> > > + using _Cat1 =
> __decltype(std::__iter_concept_or_category<_II1>());
> > > + using _Cat2 =
> __decltype(std::__iter_concept_or_category<_II2>());
> > > using _RAIters = __and_<is_same<_Cat1, _RATag>,
> is_same<_Cat2, _RATag>>;
> > > if constexpr (_RAIters::value)
> > > {
> > > diff --git
> a/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
> b/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
> > > index 7c80e1423e45..da5945727093 100644
> > > --- a/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
> > > +++ b/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
> > > @@ -317,6 +317,76 @@ namespace __detail
> > >
> > > #endif // C++11
> > >
> > > +#if __glibcxx_algorithm_iterator_requirements // C++ >= 20
> > > + template<typename _Iter>
> > > + consteval auto
> > > + __iter_concept_or_category()
> > > + {
> > > + if constexpr
> (__detail::__promotable_iterator<_Iter>)
> > > + {
> > > + using __type =
> __detail::__iter_traits<_Iter>::iterator_concept;
> > > + if constexpr (derived_from<__type,
> random_access_iterator_tag>)
> > > + return random_access_iterator_tag{};
> > > + else
> > > + return __type{};
> > > + }
> > > + else
> > > + return typename
> iterator_traits<_Iter>::iterator_category{};
> > > + }
> > > +
> > > + template<typename _Iter>
> > > + __attribute__((__always_inline__))
> > > + constexpr auto
> > > + __iter_concept_or_category(const _Iter&)
> > > + { return std::__iter_concept_or_category<_Iter>(); }
> > > +#else
> > > + template<typename _Iter>
> > > + __attribute__((__always_inline__))
> > > + inline _GLIBCXX_CONSTEXPR
> > > + typename iterator_traits<_Iter>::iterator_category
> > > + __iter_concept_or_category()
> > > + { return typename
> iterator_traits<_Iter>::iterator_category(); }
> > > +
> > > + template<typename _Iter>
> > > + __attribute__((__always_inline__))
> > > + inline _GLIBCXX_CONSTEXPR
> > > + typename iterator_traits<_Iter>::iterator_category
> > > + __iter_concept_or_category(const _Iter&)
> > > + { return typename
> iterator_traits<_Iter>::iterator_category(); }
> > > +#endif
> > > +
> > > +#if __cplusplus >= 201103L
> > > + // Like __is_random_access_iter, but based off of
> __iter_concept_or_category
> > > + // instead of iterator_traits::iterator_category.
> > > + template<typename _Iter,
> > > + typename _Cat =
> __decltype(__iter_concept_or_category<_Iter>())>
> > > + struct __is_any_random_access_iter
> > > + : is_base_of<random_access_iterator_tag, _Cat>
> > > + { enum { __value = __is_any_random_access_iter::value
> }; };
> > > +#else
> > > + template<typename _Iter,
> > > + typename _Cat =
> __decltype(__iter_concept_or_category<_Iter>())>
> > > + struct __is_any_random_access_iter
> > > + { enum { __value =
> __is_base_of(random_access_iterator_tag, _Cat) }; };
> > > +#endif
> > > +
> > > +#if __cplusplus >= 202002L
> > > + // A wrapper around ranges::iter_move that also
> converts to the iterator's
> > > + // value type.
> > > + template<typename _Iter>
> > > + [[nodiscard]] constexpr iter_value_t<_Iter>
> > > + __iter_move_val(const _Iter& __it)
> > > + noexcept(noexcept(ranges::iter_move(__it)))
> > >
> > > We also need && is_nothrow_cosntructible_v<iter_value_t<_Iter>,
> iter_rvalue_reference_t<_Iter>>>,
> > > or just noexcept(iter_value_t<_Iter>(ranges::iter_move(__it)))
> > > + { return ranges::iter_move(__it); }
> > > +#else
> > > + template<typename _Iter>
> > > + _GLIBCXX_NODISCARD inline _GLIBCXX_CONSTEXPR
> > > + typename iterator_traits<_Iter>::value_type
> > > + __iter_move_val(const _Iter& __it)
> > > + _GLIBCXX_NOEXCEPT_IF(noexcept(_GLIBCXX_MOVE(*__it)))
> > >
> > > Similar here, may have _Vt as the defaulted second template
> parameter.
> >
> > Good catch. Default template arguments on function templates
> aren't
> > supported in C++98, so it seems cleanest to just have three
> definitinons
> > of __iter_move_val:
> >
> > Thanks. LGTM now.
>
> Thanks for the review.
>
> I noticed shortly after submitting this latest version that using
> __iter_move_val might introduce an extra copy in C++98 mode compared to
> using _GLIBCXX_MOVE directly, I think. I wonder how much we care?
>
I would assume that this constructor would get elided anyway, so this would
be not
observable. And we already require a copy constructor to compile.
> I guess we could defined __iter_move_val as a macro (_GLIBCXX_ITER_MOVE)
> to avoid this extra copy?
>
This would reduce a lot of boilerplace (conditional noexcept), if we define
it as
simply static_cast<iter_value_t>(ranges::iter_move), and there would be
only pre-C++20
and post-C++20 versions.
>
> >
> > -- >8 --
> >
> > Subject: [PATCH v5] libstdc++: Implement P2408R5 Ranges iterators
> as inputs to
> > non-Ranges algorithms
> >
> > changes in v5: correct __iter_move_val's noexcept-spec
> >
> > changes in v4: define the new helpers in stl_iterator_base_funcs.h
> > rather than stl_iterator_base_types.h. also define an
> __iter_move_val
> > helper
> >
> > changes v3: add inclusive_scan test using zip's proxy iterator.
> rename
> > tests from p2408r5.cc to c++20_iter.cc
> >
> > changes v2: more tests, and the one-argument version of
> > __iter_concept_or_category is now constexpr instead of
> > consteval
> >
> > -- >8 --
> >
> > PR libstdc++/113299
> >
> > libstdc++-v3/ChangeLog:
> >
> > * include/bits/deque.tcc (__copy_move_a1): Constrain with
> > __is_any_random_access_iter instead of
> __is_random_access_iter.
> > (__copy_move_backward_a1): Likewise.
> > (__equal_aux1): Likewise.
> > * include/bits/stl_algo.h (__search_n): Use
> > __iter_concept_or_category instead of __iterator_category
> > or iterator_traits::iterator_category.
> > (find_end): Likewise.
> > (__is_permutation): Likewise.
> > (for_each_n): Likewise.
> > (unique_copy): Likewise, for constant iterators.
> > (sample): Likewise, for constant iterators.
> > * include/bits/stl_algobase.h (__copy_move_a1): Adjust
> > deque-based forward declaration accordingly.
> > (__copy_move_backward_a1): Likewise.
> > (__equal_aux1): Likewise.
> > (__lexicographical_compare_impl): Use
> > __iter_concept_or_category instead of __iterator_category
> or
> > iterator_traits::iterator_category.
> > (__equal4): Likewise.
> > * include/bits/stl_iterator_base_funcs.h
> > (__iter_concept_or_category): New.
> > (__is_any_random_access_iter): New.
> > (__iter_move_val): New.
> > * include/bits/stl_uninitialized.h (uninitialized_copy_n):
> > Use __iterator_concept_or_category instead of
> > __iterator_category for the constant iterator __first.
> > (__uninitialized_copy_n_pair): Likewise.
> > * include/bits/version.def
> (algorithm_iterator_requirements):
> > Define.
> > * include/bits/version.h: Regenerate.
> > * include/std/algorithm: Provide the FTM
> > __cpp_lib_algorithm_iterator_requirements.
> > * include/std/memory: Likewise.
> > * include/std/numeric: Likewise.
> > (reduce): Use __is_any_random_access_iter instead of
> > __is_random_access_iter.
> > (transform_reduce): Likewise.
> > (inclusive_scan): Use __iter_move_val instead of std::move.
> > * testsuite/25_algorithms/find_end/c++20_iter.cc: New test.
> > * testsuite/25_algorithms/sample/c++20_iter.cc: New test.
> > * testsuite/25_algorithms/search_n/c++20_iter.cc: New test.
> > * testsuite/25_algorithms/unique_copy/c++20_iter.cc: New
> test.
> > * testsuite/26_numerics/inclusive_scan/c++20_iter.cc: New
> test.
> > ---
> > libstdc++-v3/include/bits/deque.tcc | 8 +-
> > libstdc++-v3/include/bits/stl_algo.h | 28 +++----
> > libstdc++-v3/include/bits/stl_algobase.h | 20 ++---
> > .../include/bits/stl_iterator_base_funcs.h | 75
> +++++++++++++++++++
> > libstdc++-v3/include/bits/stl_uninitialized.h | 4 +-
> > libstdc++-v3/include/bits/version.def | 9 +++
> > libstdc++-v3/include/bits/version.h | 10 +++
> > libstdc++-v3/include/std/algorithm | 1 +
> > libstdc++-v3/include/std/memory | 1 +
> > libstdc++-v3/include/std/numeric | 11 +--
> > .../25_algorithms/find_end/c++20_iter.cc | 23 ++++++
> > .../25_algorithms/sample/c++20_iter.cc | 23 ++++++
> > .../25_algorithms/search_n/c++20_iter.cc | 21 ++++++
> > .../25_algorithms/unique_copy/c++20_iter.cc | 33 ++++++++
> > .../26_numerics/inclusive_scan/c++20_iter.cc | 26 +++++++
> > 15 files changed, 258 insertions(+), 35 deletions(-)
> > create mode 100644
> libstdc++-v3/testsuite/25_algorithms/find_end/c++20_iter.cc
> > create mode 100644
> libstdc++-v3/testsuite/25_algorithms/sample/c++20_iter.cc
> > create mode 100644
> libstdc++-v3/testsuite/25_algorithms/search_n/c++20_iter.cc
> > create mode 100644
> libstdc++-v3/testsuite/25_algorithms/unique_copy/c++20_iter.cc
> > create mode 100644
> libstdc++-v3/testsuite/26_numerics/inclusive_scan/c++20_iter.cc
> >
> > diff --git a/libstdc++-v3/include/bits/deque.tcc
> b/libstdc++-v3/include/bits/deque.tcc
> > index 20b23fffc9e1..e409f3a3fc57 100644
> > --- a/libstdc++-v3/include/bits/deque.tcc
> > +++ b/libstdc++-v3/include/bits/deque.tcc
> > @@ -1225,7 +1225,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> >
> > template<bool _IsMove, typename _II, typename _Tp>
> > typename __gnu_cxx::__enable_if<
> > - __is_random_access_iter<_II>::__value,
> > + __is_any_random_access_iter<_II>::__value,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*> >::__type
> > __copy_move_a1(_II __first, _II __last,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&,
> _Tp*> __result)
> > @@ -1347,7 +1347,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> >
> > template<bool _IsMove, typename _II, typename _Tp>
> > typename __gnu_cxx::__enable_if<
> > - __is_random_access_iter<_II>::__value,
> > + __is_any_random_access_iter<_II>::__value,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*> >::__type
> > __copy_move_backward_a1(_II __first, _II __last,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*>
> __result)
> > @@ -1406,7 +1406,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> >
> > template<typename _Tp, typename _Ref, typename _Ptr, typename
> _II>
> > typename __gnu_cxx::__enable_if<
> > - __is_random_access_iter<_II>::__value, bool>::__type
> > + __is_any_random_access_iter<_II>::__value, bool>::__type
> > __equal_aux1(_GLIBCXX_STD_C::_Deque_iterator<_Tp, _Ref, _Ptr>
> __first1,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Ref, _Ptr>
> __last1,
> > _II __first2)
> > @@ -1422,7 +1422,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> >
> > template<typename _II, typename _Tp, typename _Ref, typename
> _Ptr>
> > typename __gnu_cxx::__enable_if<
> > - __is_random_access_iter<_II>::__value, bool>::__type
> > + __is_any_random_access_iter<_II>::__value, bool>::__type
> > __equal_aux1(_II __first1, _II __last1,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Ref, _Ptr>
> __first2)
> > {
> > diff --git a/libstdc++-v3/include/bits/stl_algo.h
> b/libstdc++-v3/include/bits/stl_algo.h
> > index bbd1800af779..0d8f7af9d272 100644
> > --- a/libstdc++-v3/include/bits/stl_algo.h
> > +++ b/libstdc++-v3/include/bits/stl_algo.h
> > @@ -226,7 +226,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > return std::__find_if(__first, __last, __unary_pred);
> >
> > return std::__search_n_aux(__first, __last, __count,
> __unary_pred,
> > -
> std::__iterator_category(__first));
> > +
> std::__iter_concept_or_category(__first));
> > }
> >
> > // find_end for forward iterators.
> > @@ -337,8 +337,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > __glibcxx_requires_valid_range(__first2, __last2);
> >
> > return std::__find_end(__first1, __last1, __first2, __last2,
> > - std::__iterator_category(__first1),
> > - std::__iterator_category(__first2),
> > +
> std::__iter_concept_or_category(__first1),
> > +
> std::__iter_concept_or_category(__first2),
> > __gnu_cxx::__ops::equal_to());
> > }
> >
> > @@ -388,8 +388,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > __glibcxx_requires_valid_range(__first2, __last2);
> >
> > return std::__find_end(__first1, __last1, __first2, __last2,
> > - std::__iterator_category(__first1),
> > - std::__iterator_category(__first2),
> > +
> std::__iter_concept_or_category(__first1),
> > +
> std::__iter_concept_or_category(__first2),
> > __comp);
> > }
> >
> > @@ -3495,9 +3495,9 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
> > _BinaryPredicate __pred)
> > {
> > using _Cat1
> > - = typename
> iterator_traits<_ForwardIterator1>::iterator_category;
> > + =
> __decltype(std::__iter_concept_or_category<_ForwardIterator1>());
> > using _Cat2
> > - = typename
> iterator_traits<_ForwardIterator2>::iterator_category;
> > + =
> __decltype(std::__iter_concept_or_category<_ForwardIterator2>());
> > using _It1_is_RA = is_same<_Cat1,
> random_access_iterator_tag>;
> > using _It2_is_RA = is_same<_Cat2,
> random_access_iterator_tag>;
> > constexpr bool __ra_iters = __and_<_It1_is_RA,
> _It2_is_RA>::value;
> > @@ -3800,7 +3800,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > for_each_n(_InputIterator __first, _Size __n, _Function __f)
> > {
> > auto __n2 = std::__size_to_integer(__n);
> > - using _Cat = typename
> iterator_traits<_InputIterator>::iterator_category;
> > + using _Cat =
> __decltype(std::__iter_concept_or_category<_InputIterator>());
> > if constexpr (is_base_of_v<random_access_iterator_tag,
> _Cat>)
> > {
> > if (__n2 <= 0)
> > @@ -4450,7 +4450,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > return __result;
> > return std::__unique_copy(__first, __last, __result,
> > __gnu_cxx::__ops::equal_to(),
> > - std::__iterator_category(__first));
> > +
> std::__iter_concept_or_category(__first));
> > }
> >
> > /**
> > @@ -4491,7 +4491,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > if (__first == __last)
> > return __result;
> > return std::__unique_copy(__first, __last, __result,
> __binary_pred,
> > - std::__iterator_category(__first));
> > +
> std::__iter_concept_or_category(__first));
> > }
> >
> > #if __cplusplus <= 201103L || _GLIBCXX_USE_DEPRECATED
> > @@ -5881,10 +5881,10 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > _SampleIterator __out, _Distance __n,
> > _UniformRandomBitGenerator&& __g)
> > {
> > - using __pop_cat = typename
> > -
> std::iterator_traits<_PopulationIterator>::iterator_category;
> > - using __samp_cat = typename
> > - std::iterator_traits<_SampleIterator>::iterator_category;
> > + using __pop_cat
> > + =
> __decltype(std::__iter_concept_or_category<_PopulationIterator>());
> > + using __samp_cat
> > + = typename
> iterator_traits<_SampleIterator>::iterator_category;
> >
> > static_assert(
> > __or_<is_convertible<__pop_cat, forward_iterator_tag>,
> > diff --git a/libstdc++-v3/include/bits/stl_algobase.h
> b/libstdc++-v3/include/bits/stl_algobase.h
> > index 443cbef76dee..701910afd837 100644
> > --- a/libstdc++-v3/include/bits/stl_algobase.h
> > +++ b/libstdc++-v3/include/bits/stl_algobase.h
> > @@ -480,7 +480,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> >
> > template<bool _IsMove, typename _II, typename _Tp>
> > typename __gnu_cxx::__enable_if<
> > - __is_random_access_iter<_II>::__value,
> > + __is_any_random_access_iter<_II>::__value,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*> >::__type
> > __copy_move_a1(_II, _II, _GLIBCXX_STD_C::_Deque_iterator<_Tp,
> _Tp&, _Tp*>);
> >
> > @@ -769,7 +769,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> >
> > template<bool _IsMove, typename _II, typename _Tp>
> > typename __gnu_cxx::__enable_if<
> > - __is_random_access_iter<_II>::__value,
> > + __is_any_random_access_iter<_II>::__value,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Tp&, _Tp*> >::__type
> > __copy_move_backward_a1(_II, _II,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp,
> _Tp&, _Tp*>);
> > @@ -1219,7 +1219,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> >
> > template<typename _Tp, typename _Ref, typename _Ptr, typename
> _II>
> > typename __gnu_cxx::__enable_if<
> > - __is_random_access_iter<_II>::__value, bool>::__type
> > + __is_any_random_access_iter<_II>::__value, bool>::__type
> > __equal_aux1(_GLIBCXX_STD_C::_Deque_iterator<_Tp, _Ref, _Ptr>,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Ref, _Ptr>,
> > _II);
> > @@ -1233,7 +1233,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> >
> > template<typename _II, typename _Tp, typename _Ref, typename
> _Ptr>
> > typename __gnu_cxx::__enable_if<
> > - __is_random_access_iter<_II>::__value, bool>::__type
> > + __is_any_random_access_iter<_II>::__value, bool>::__type
> > __equal_aux1(_II, _II,
> > _GLIBCXX_STD_C::_Deque_iterator<_Tp, _Ref, _Ptr>);
> >
> > @@ -1332,8 +1332,8 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
> > _II2 __first2, _II2 __last2,
> > _Compare __comp)
> > {
> > - typedef typename iterator_traits<_II1>::iterator_category
> _Category1;
> > - typedef typename iterator_traits<_II2>::iterator_category
> _Category2;
> > + typedef __decltype(std::__iter_concept_or_category<_II1>())
> _Category1;
> > + typedef __decltype(std::__iter_concept_or_category<_II2>())
> _Category2;
> > typedef std::__lc_rai<_Category1, _Category2> __rai_type;
> >
> > __last1 = __rai_type::__newlast1(__first1, __last1,
> __first2, __last2);
> > @@ -1649,8 +1649,8 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > __equal4(_II1 __first1, _II1 __last1, _II2 __first2, _II2
> __last2)
> > {
> > using _RATag = random_access_iterator_tag;
> > - using _Cat1 = typename
> iterator_traits<_II1>::iterator_category;
> > - using _Cat2 = typename
> iterator_traits<_II2>::iterator_category;
> > + using _Cat1 =
> __decltype(std::__iter_concept_or_category<_II1>());
> > + using _Cat2 =
> __decltype(std::__iter_concept_or_category<_II2>());
> > using _RAIters = __and_<is_same<_Cat1, _RATag>,
> is_same<_Cat2, _RATag>>;
> > if constexpr (_RAIters::value)
> > {
> > @@ -1676,8 +1676,8 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
> > _BinaryPredicate __binary_pred)
> > {
> > using _RATag = random_access_iterator_tag;
> > - using _Cat1 = typename
> iterator_traits<_II1>::iterator_category;
> > - using _Cat2 = typename
> iterator_traits<_II2>::iterator_category;
> > + using _Cat1 =
> __decltype(std::__iter_concept_or_category<_II1>());
> > + using _Cat2 =
> __decltype(std::__iter_concept_or_category<_II2>());
> > using _RAIters = __and_<is_same<_Cat1, _RATag>,
> is_same<_Cat2, _RATag>>;
> > if constexpr (_RAIters::value)
> > {
> > diff --git a/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
> b/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
> > index 7c80e1423e45..47fc4c84490c 100644
> > --- a/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
> > +++ b/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
> > @@ -317,6 +317,81 @@ namespace __detail
> >
> > #endif // C++11
> >
> > +#if __glibcxx_algorithm_iterator_requirements // C++ >= 20
> > + template<typename _Iter>
> > + consteval auto
> > + __iter_concept_or_category()
> > + {
> > + if constexpr (__detail::__promotable_iterator<_Iter>)
> > + {
> > + using __type =
> __detail::__iter_traits<_Iter>::iterator_concept;
> > + if constexpr (derived_from<__type,
> random_access_iterator_tag>)
> > + return random_access_iterator_tag{};
> > + else
> > + return __type{};
> > + }
> > + else
> > + return typename
> iterator_traits<_Iter>::iterator_category{};
> > + }
> > +
> > + template<typename _Iter>
> > + __attribute__((__always_inline__))
> > + constexpr auto
> > + __iter_concept_or_category(const _Iter&)
> > + { return std::__iter_concept_or_category<_Iter>(); }
> > +#else
> > + template<typename _Iter>
> > + __attribute__((__always_inline__))
> > + inline _GLIBCXX_CONSTEXPR
> > + typename iterator_traits<_Iter>::iterator_category
> > + __iter_concept_or_category()
> > + { return typename
> iterator_traits<_Iter>::iterator_category(); }
> > +
> > + template<typename _Iter>
> > + __attribute__((__always_inline__))
> > + inline _GLIBCXX_CONSTEXPR
> > + typename iterator_traits<_Iter>::iterator_category
> > + __iter_concept_or_category(const _Iter&)
> > + { return typename
> iterator_traits<_Iter>::iterator_category(); }
> > +#endif
> > +
> > +#if __cplusplus >= 201103L
> > + // Like __is_random_access_iter, but based off of
> __iter_concept_or_category
> > + // instead of iterator_traits::iterator_category.
> > + template<typename _Iter,
> > + typename _Cat =
> __decltype(__iter_concept_or_category<_Iter>())>
> > + struct __is_any_random_access_iter
> > + : is_base_of<random_access_iterator_tag, _Cat>
> > + { enum { __value = __is_any_random_access_iter::value }; };
> > +#else
> > + template<typename _Iter,
> > + typename _Cat =
> __decltype(__iter_concept_or_category<_Iter>())>
> > + struct __is_any_random_access_iter
> > + { enum { __value = __is_base_of(random_access_iterator_tag,
> _Cat) }; };
> > +#endif
> > +
> > +#if __cplusplus >= 202002L
> > + // A wrapper around ranges::iter_move that also converts to the
> iterator's
> > + // value type.
> > + template<typename _Iter>
> > + [[nodiscard]] constexpr iter_value_t<_Iter>
> > + __iter_move_val(const _Iter& __it)
> > +
> noexcept(noexcept(iter_value_t<_Iter>(ranges::iter_move(__it))))
> > + { return ranges::iter_move(__it); }
> > +#elif __cplusplus >= 201103L
> > + template<typename _Iter,
> > + typename _Tp = typename
> iterator_traits<_Iter>::value_type>
> > + [[nodiscard]] constexpr _Tp
> > + __iter_move_val(const _Iter& __it)
> > + noexcept(noexcept(_Tp(std::move(*__it))))
> > + { return std::move(*__it); }
> > +#else
> > + template<typename _Iter>
> > + inline typename iterator_traits<_Iter>::value_type
> > + __iter_move_val(const _Iter& __it)
> > + { return *__it; }
> > +#endif
> > +
> > _GLIBCXX_END_NAMESPACE_VERSION
> > } // namespace
> >
> > diff --git a/libstdc++-v3/include/bits/stl_uninitialized.h
> b/libstdc++-v3/include/bits/stl_uninitialized.h
> > index 70a564659814..96f740e86e7b 100644
> > --- a/libstdc++-v3/include/bits/stl_uninitialized.h
> > +++ b/libstdc++-v3/include/bits/stl_uninitialized.h
> > @@ -1177,7 +1177,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > uninitialized_copy_n(_InputIterator __first, _Size __n,
> > _ForwardIterator __result)
> > { return std::__uninitialized_copy_n(__first, __n, __result,
> > -
> std::__iterator_category(__first)); }
> > +
> std::__iter_concept_or_category(__first)); }
> >
> > /// @cond undocumented
> > template<typename _InputIterator, typename _Size, typename
> _ForwardIterator>
> > @@ -1188,7 +1188,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > {
> > return
> > std::__uninitialized_copy_n_pair(__first, __n, __result,
> > -
> std::__iterator_category(__first));
> > +
> std::__iter_concept_or_category(__first));
> > }
> > /// @endcond
> > #endif
> > diff --git a/libstdc++-v3/include/bits/version.def
> b/libstdc++-v3/include/bits/version.def
> > index 29ecf15c7e39..9177af610b16 100644
> > --- a/libstdc++-v3/include/bits/version.def
> > +++ b/libstdc++-v3/include/bits/version.def
> > @@ -1972,6 +1972,15 @@ ftms = {
> > };
> > };
> >
> > +ftms = {
> > + name = algorithm_iterator_requirements;
> > + values = {
> > + v = 202207;
> > + // P2408R5 is a C++23 feature, but we support it in C++20.
> > + cxxmin = 20;
> > + };
> > +};
> > +
> > ftms = {
> > name = algorithm_default_value_type;
> > values = {
> > diff --git a/libstdc++-v3/include/bits/version.h
> b/libstdc++-v3/include/bits/version.h
> > index 5901d27113d7..3a930db2239b 100644
> > --- a/libstdc++-v3/include/bits/version.h
> > +++ b/libstdc++-v3/include/bits/version.h
> > @@ -2206,6 +2206,16 @@
> > #endif /* !defined(__cpp_lib_observable_checkpoint) */
> > #undef __glibcxx_want_observable_checkpoint
> >
> > +#if !defined(__cpp_lib_algorithm_iterator_requirements)
> > +# if (__cplusplus >= 202002L)
> > +# define __glibcxx_algorithm_iterator_requirements 202207L
> > +# if defined(__glibcxx_want_all) ||
> defined(__glibcxx_want_algorithm_iterator_requirements)
> > +# define __cpp_lib_algorithm_iterator_requirements 202207L
> > +# endif
> > +# endif
> > +#endif /* !defined(__cpp_lib_algorithm_iterator_requirements) */
> > +#undef __glibcxx_want_algorithm_iterator_requirements
> > +
> > #if !defined(__cpp_lib_algorithm_default_value_type)
> > # if (__cplusplus > 202302L)
> > # define __glibcxx_algorithm_default_value_type 202403L
> > diff --git a/libstdc++-v3/include/std/algorithm
> b/libstdc++-v3/include/std/algorithm
> > index 1563cdf2b17c..a39474df8b1d 100644
> > --- a/libstdc++-v3/include/std/algorithm
> > +++ b/libstdc++-v3/include/std/algorithm
> > @@ -66,6 +66,7 @@
> > #endif
> >
> > #define __glibcxx_want_algorithm_default_value_type
> > +#define __glibcxx_want_algorithm_iterator_requirements
> > #define __glibcxx_want_clamp
> > #define __glibcxx_want_constexpr_algorithms
> > #define __glibcxx_want_freestanding_algorithm
> > diff --git a/libstdc++-v3/include/std/memory
> b/libstdc++-v3/include/std/memory
> > index 9763760b8d61..52056d2f02a5 100644
> > --- a/libstdc++-v3/include/std/memory
> > +++ b/libstdc++-v3/include/std/memory
> > @@ -102,6 +102,7 @@
> > #endif
> >
> > #define __glibcxx_want_addressof_constexpr
> > +#define __glibcxx_want_algorithm_iterator_requirements
> > #define __glibcxx_want_allocator_traits_is_always_equal
> > #define __glibcxx_want_assume_aligned
> > #define __glibcxx_want_atomic_shared_ptr
> > diff --git a/libstdc++-v3/include/std/numeric
> b/libstdc++-v3/include/std/numeric
> > index cbabf031216e..c9faac485050 100644
> > --- a/libstdc++-v3/include/std/numeric
> > +++ b/libstdc++-v3/include/std/numeric
> > @@ -81,6 +81,7 @@
> > # include <limits>
> > #endif
> >
> > +#define __glibcxx_want_algorithm_iterator_requirements
> > #define __glibcxx_want_constexpr_numeric
> > #define __glibcxx_want_gcd
> > #define __glibcxx_want_gcd_lcm
> > @@ -298,7 +299,7 @@ namespace __detail
> > static_assert(is_invocable_r_v<_Tp, _BinaryOperation&,
> __ref, _Tp&>);
> > static_assert(is_invocable_r_v<_Tp, _BinaryOperation&,
> _Tp&, _Tp&>);
> > static_assert(is_invocable_r_v<_Tp, _BinaryOperation&,
> __ref, __ref>);
> > - if constexpr
> (__is_random_access_iter<_InputIterator>::value)
> > + if constexpr
> (__is_any_random_access_iter<_InputIterator>::value)
> > {
> > while ((__last - __first) >= 4)
> > {
> > @@ -378,8 +379,8 @@ namespace __detail
> > _BinaryOperation1 __binary_op1,
> > _BinaryOperation2 __binary_op2)
> > {
> > - if constexpr
> (__and_v<__is_random_access_iter<_InputIterator1>,
> > -
> __is_random_access_iter<_InputIterator2>>)
> > + if constexpr
> (__and_v<__is_any_random_access_iter<_InputIterator1>,
> > +
> __is_any_random_access_iter<_InputIterator2>>)
> > {
> > while ((__last1 - __first1) >= 4)
> > {
> > @@ -445,7 +446,7 @@ namespace __detail
> > transform_reduce(_InputIterator __first, _InputIterator
> __last, _Tp __init,
> > _BinaryOperation __binary_op, _UnaryOperation
> __unary_op)
> > {
> > - if constexpr
> (__is_random_access_iter<_InputIterator>::value)
> > + if constexpr
> (__is_any_random_access_iter<_InputIterator>::value)
> > {
> > while ((__last - __first) >= 4)
> > {
> > @@ -582,7 +583,7 @@ namespace __detail
> > {
> > if (__first != __last)
> > {
> > - auto __init = std::move(*__first);
> > + auto __init = std::__iter_move_val(__first);
> > *__result++ = __init;
> > ++__first;
> > if (__first != __last)
> > diff --git
> a/libstdc++-v3/testsuite/25_algorithms/find_end/c++20_iter.cc
> b/libstdc++-v3/testsuite/25_algorithms/find_end/c++20_iter.cc
> > new file mode 100644
> > index 000000000000..6bd1cead1c36
> > --- /dev/null
> > +++ b/libstdc++-v3/testsuite/25_algorithms/find_end/c++20_iter.cc
> > @@ -0,0 +1,23 @@
> > +// Verify std::find_end is C++20 iterator aware as per P2408R5.
> > +// { dg-do compile { target c++20 } }
> > +
> > +#include <algorithm>
> > +#include <ranges>
> > +#include <testsuite_hooks.h>
> > +
> > +constexpr bool
> > +test01()
> > +{
> > + auto r = std::views::iota(0, 10);
> > + auto s = std::views::iota(5, 10);
> > + auto it = r.begin();
> > + auto jt = s.begin();
> > + static_assert( std::random_access_iterator<decltype(it)>);
> > + static_assert(
> std::same_as<std::iterator_traits<decltype(it)>::iterator_category,
> > + std::input_iterator_tag> );
> > + it = std::find_end(it, it+10, jt, jt+5);
> > + VERIFY( it == r.begin() + 5 );
> > + return true;
> > +}
> > +
> > +static_assert(test01());
> > diff --git
> a/libstdc++-v3/testsuite/25_algorithms/sample/c++20_iter.cc
> b/libstdc++-v3/testsuite/25_algorithms/sample/c++20_iter.cc
> > new file mode 100644
> > index 000000000000..3933b3a2a2c2
> > --- /dev/null
> > +++ b/libstdc++-v3/testsuite/25_algorithms/sample/c++20_iter.cc
> > @@ -0,0 +1,23 @@
> > +// Verify std::sample is C++20 iterator aware as per P2408R5.
> > +// { dg-do compile { target c++20 } }
> > +
> > +#include <algorithm>
> > +#include <random>
> > +#include <ranges>
> > +#include <testsuite_hooks.h>
> > +#include <testsuite_iterators.h>
> > +
> > +std::mt19937 rng;
> > +
> > +void
> > +test01()
> > +{
> > + auto r = std::views::iota(10);
> > + auto it = r.begin();
> > + static_assert( std::random_access_iterator<decltype(it)>);
> > + static_assert(
> std::same_as<std::iterator_traits<decltype(it)>::iterator_category,
> > + std::input_iterator_tag> );
> > + int buf[10];
> > + __gnu_test::output_container<int> s(buf);
> > + std::sample(it, it+10, s.begin(), 10, rng);
> > +}
> > diff --git
> a/libstdc++-v3/testsuite/25_algorithms/search_n/c++20_iter.cc
> b/libstdc++-v3/testsuite/25_algorithms/search_n/c++20_iter.cc
> > new file mode 100644
> > index 000000000000..9787358e6674
> > --- /dev/null
> > +++ b/libstdc++-v3/testsuite/25_algorithms/search_n/c++20_iter.cc
> > @@ -0,0 +1,21 @@
> > +// Verify std::search_n is Ranges iterator aware as per P2408R5.
> > +// { dg-do compile { target c++20 } }
> > +
> > +#include <algorithm>
> > +#include <ranges>
> > +#include <testsuite_hooks.h>
> > +
> > +constexpr bool
> > +test01()
> > +{
> > + auto r = std::views::iota(0, 10);
> > + auto it = r.begin();
> > + static_assert( std::random_access_iterator<decltype(it)>);
> > + static_assert(
> std::same_as<std::iterator_traits<decltype(it)>::iterator_category,
> > + std::input_iterator_tag> );
> > + it = std::search_n(it, it+10, 1, 5);
> > + VERIFY( it == r.begin() + 5 );
> > + return true;
> > +}
> > +
> > +static_assert(test01());
> > diff --git
> a/libstdc++-v3/testsuite/25_algorithms/unique_copy/c++20_iter.cc
> b/libstdc++-v3/testsuite/25_algorithms/unique_copy/c++20_iter.cc
> > new file mode 100644
> > index 000000000000..20017ced8672
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/25_algorithms/unique_copy/c++20_iter.cc
> > @@ -0,0 +1,33 @@
> > +// Verify std::unique_copy is C++20 iterator aware as per P2408R5.
> > +// { dg-do compile { target c++20 } }
> > +
> > +#include <algorithm>
> > +#include <ranges>
> > +#include <testsuite_hooks.h>
> > +#include <testsuite_iterators.h>
> > +
> > +struct noncopyable
> > +{
> > + constexpr operator int() { return 42; }
> > + noncopyable() = default;
> > + noncopyable(const noncopyable&) = delete;
> > + noncopyable& operator=(const noncopyable&) = delete;
> > + friend auto operator<=>(const noncopyable&, const noncopyable&)
> = default;
> > +};
> > +
> > +constexpr bool
> > +test01()
> > +{
> > + auto r = std::views::iota(10)
> > + | std::views::transform([](int) { return noncopyable{}; });
> > + auto it = r.begin();
> > + static_assert( std::random_access_iterator<decltype(it)>);
> > + static_assert(
> std::same_as<std::iterator_traits<decltype(it)>::iterator_category,
> > + std::input_iterator_tag> );
> > + int buf[10];
> > + __gnu_test::input_container<int> s(buf);
> > + auto jt = std::unique_copy(it, it+10, s.begin());
> > + return true;
> > +}
> > +
> > +static_assert(test01());
> > diff --git
> a/libstdc++-v3/testsuite/26_numerics/inclusive_scan/c++20_iter.cc
> b/libstdc++-v3/testsuite/26_numerics/inclusive_scan/c++20_iter.cc
> > new file mode 100644
> > index 000000000000..d8f2781fc669
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/26_numerics/inclusive_scan/c++20_iter.cc
> > @@ -0,0 +1,26 @@
> > +// Verify std::inclusive_scan is C++20 iterator aware as per
> P2408R5.
> > +// { dg-do compile { target c++23 } }
> > +
> > +#include <numeric>
> > +#include <ranges>
> > +#include <testsuite_hooks.h>
> > +
> > +constexpr bool
> > +test01()
> > +{
> > + int x[10] = {1,2,3,4,5,6,7,8,9,10};
> > + auto r = std::views::zip(x);
> > + auto it = r.begin();
> > + static_assert( std::random_access_iterator<decltype(it)>);
> > + static_assert(
> std::same_as<std::iterator_traits<decltype(it)>::iterator_category,
> > + std::input_iterator_tag> );
> > + std::tuple<int> y[10];
> > + std::inclusive_scan(it, it+10, y,
> > + [](std::tuple<int> a, std::tuple<int> b) ->
> std::tuple<int> {
> > + return std::get<0>(a) + std::get<0>(b);
> > + });
> > + VERIFY( std::get<0>(y[9]) == 55 );
> > + return true;
> > +}
> > +
> > +static_assert(test01());
> > --
> > 2.52.0.51.gdebbc87557
> >
> >
> >
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