On Wed, 8 Mar 2023 at 16:47, Patrick Palka via Libstdc++
<libstd...@gcc.gnu.org> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk and perhaps
> backports?
Yes for all.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/stl_iterator.h (move_iterator::_S_iter_concept):
> Define.
> (__cpp_lib_move_iterator_concept): Define for C++20.
> (move_iterator::iterator_concept): Strengthen as per P2520R0.
> * include/std/version (__cpp_lib_move_iterator_concept): Define
> for C++20.
> * testsuite/24_iterators/move_iterator/p2520r0.cc: New test.
> ---
> libstdc++-v3/include/bits/stl_iterator.h | 20 +++++++++-
> libstdc++-v3/include/std/version | 1 +
> .../24_iterators/move_iterator/p2520r0.cc | 37 +++++++++++++++++++
> 3 files changed, 57 insertions(+), 1 deletion(-)
> create mode 100644
> libstdc++-v3/testsuite/24_iterators/move_iterator/p2520r0.cc
>
> diff --git a/libstdc++-v3/include/bits/stl_iterator.h
> b/libstdc++-v3/include/bits/stl_iterator.h
> index c20dc9ecac5..a6a09dbac16 100644
> --- a/libstdc++-v3/include/bits/stl_iterator.h
> +++ b/libstdc++-v3/include/bits/stl_iterator.h
> @@ -1465,11 +1465,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> && convertible_to<const _Iter2&, _Iterator>;
> #endif
>
> +#if __cplusplus > 201703L && __cpp_lib_concepts
> + static auto
> + _S_iter_concept()
> + {
> + if constexpr (random_access_iterator<_Iterator>)
> + return random_access_iterator_tag{};
> + else if constexpr (bidirectional_iterator<_Iterator>)
> + return bidirectional_iterator_tag{};
> + else if constexpr (forward_iterator<_Iterator>)
> + return forward_iterator_tag{};
> + else
> + return input_iterator_tag{};
> + }
> +#endif
> +
> public:
> using iterator_type = _Iterator;
>
> #if __cplusplus > 201703L && __cpp_lib_concepts
> - using iterator_concept = input_iterator_tag;
> + // This is P2520R0, a C++23 change, but we treat it as a DR against
> C++20.
> +# define __cpp_lib_move_iterator_concept 202207L
> + using iterator_concept = decltype(_S_iter_concept());
> +
> // iterator_category defined in __move_iter_cat
> using value_type = iter_value_t<_Iterator>;
> using difference_type = iter_difference_t<_Iterator>;
> diff --git a/libstdc++-v3/include/std/version
> b/libstdc++-v3/include/std/version
> index 871d30db5b3..25ebfc3e512 100644
> --- a/libstdc++-v3/include/std/version
> +++ b/libstdc++-v3/include/std/version
> @@ -289,6 +289,7 @@
> #define __cpp_lib_polymorphic_allocator 201902L
> #if __cpp_lib_concepts
> # define __cpp_lib_ranges 202110L
> +# define __cpp_lib_move_iterator_concept 202207L
> #endif
> #if __cpp_lib_atomic_wait || _GLIBCXX_HAVE_POSIX_SEMAPHORE
> # define __cpp_lib_semaphore 201907L
> diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/p2520r0.cc
> b/libstdc++-v3/testsuite/24_iterators/move_iterator/p2520r0.cc
> new file mode 100644
> index 00000000000..883d6cc09e0
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/p2520r0.cc
> @@ -0,0 +1,37 @@
> +// { dg-options "-std=gnu++20" }
> +// { dg-do compile { target c++20 } }
> +
> +// Verify P2520R0 changes to move_iterator's iterator_concept, which we treat
> +// as a DR against C++20.
> +
> +#include <iterator>
> +#if __cpp_lib_move_iterator_concept != 202207L
> +# error "Feature-test macro __cpp_lib_move_iterator_concept has wrong value
> in <iterator>"
> +#endif
> +
> +#undef __cpp_lib_move_iterator_concept
> +#include <version>
> +#if __cpp_lib_move_iterator_concept != 202207L
> +# error "Feature-test macro __cpp_lib_move_iterator_concept has wrong value
> in <version>"
> +#endif
> +
> +#include <testsuite_iterators.h>
> +
> +using __gnu_test::test_input_range;
> +using __gnu_test::test_forward_range;
> +using __gnu_test::test_bidirectional_range;
> +using __gnu_test::test_random_access_range;
> +
> +using ty1 =
> std::move_iterator<decltype(std::declval<test_input_range<int>&>().begin())>;
> +static_assert(std::same_as<ty1::iterator_concept, std::input_iterator_tag>);
> +
> +using ty2 =
> std::move_iterator<decltype(std::declval<test_forward_range<int>&>().begin())>;
> +static_assert(std::same_as<ty2::iterator_concept,
> std::forward_iterator_tag>);
> +
> +using ty3 =
> std::move_iterator<decltype(std::declval<test_bidirectional_range<int>&>().begin())>;
> +static_assert(std::same_as<ty3::iterator_concept,
> std::bidirectional_iterator_tag>);
> +
> +using ty4 =
> std::move_iterator<decltype(std::declval<test_random_access_range<int>&>().begin())>;
> +static_assert(std::same_as<ty4::iterator_concept,
> std::random_access_iterator_tag>);
> +
> +static_assert(std::random_access_iterator<std::move_iterator<int*>>);
> --
> 2.40.0.rc0.57.g454dfcbddf
>
