include/__mdspan/mdspan.h - llvm-project/libcxx - Git at Google

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //                        Kokkos v. 4.0
 //       Copyright (2022) National Technology & Engineering
 //               Solutions of Sandia, LLC (NTESS).
 //
 // Under the terms of Contract DE-NA0003525 with NTESS,
 // the U.S. Government retains certain rights in this software.
 //
 //===---------------------------------------------------------------------===//

 #ifndef _LIBCPP___MDSPAN_MDSPAN_H
 #define _LIBCPP___MDSPAN_MDSPAN_H

 #include <__assert>
 #include <__config>
 #include <__fwd/mdspan.h>
 #include <__mdspan/default_accessor.h>
 #include <__mdspan/extents.h>
 #include <__type_traits/extent.h>
 #include <__type_traits/is_abstract.h>
 #include <__type_traits/is_array.h>
 #include <__type_traits/is_constructible.h>
 #include <__type_traits/is_convertible.h>
 #include <__type_traits/is_nothrow_constructible.h>
 #include <__type_traits/is_pointer.h>
 #include <__type_traits/is_same.h>
 #include <__type_traits/rank.h>
 #include <__type_traits/remove_all_extents.h>
 #include <__type_traits/remove_cv.h>
 #include <__type_traits/remove_pointer.h>
 #include <__type_traits/remove_reference.h>
 #include <__utility/integer_sequence.h>
 #include <array>
 #include <cinttypes>
 #include <cstddef>
 #include <limits>
 #include <span>

 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>

 _LIBCPP_BEGIN_NAMESPACE_STD

 #if _LIBCPP_STD_VER >= 23

 // Helper for lightweight test checking that one did pass a layout policy as LayoutPolicy template argument
 namespace __mdspan_detail {
 template <class _Layout, class _Extents>
 concept __has_invalid_mapping = !requires { typename _Layout::template mapping<_Extents>; };
 } // namespace __mdspan_detail

 template <class _ElementType,
           class _Extents,
           class _LayoutPolicy   = layout_right,
           class _AccessorPolicy = default_accessor<_ElementType> >
 class mdspan {
 private:
   static_assert(__mdspan_detail::__is_extents_v<_Extents>,
                 "mdspan: Extents template parameter must be a specialization of extents.");
   static_assert(!is_array_v<_ElementType>, "mdspan: ElementType template parameter may not be an array type");
   static_assert(!is_abstract_v<_ElementType>, "mdspan: ElementType template parameter may not be an abstract class");
   static_assert(is_same_v<_ElementType, typename _AccessorPolicy::element_type>,
                 "mdspan: ElementType template parameter must match AccessorPolicy::element_type");
   static_assert(!__mdspan_detail::__has_invalid_mapping<_LayoutPolicy, _Extents>,
                 "mdspan: LayoutPolicy template parameter is invalid. A common mistake is to pass a layout mapping "
                 "instead of a layout policy");

 public:
   using extents_type     = _Extents;
   using layout_type      = _LayoutPolicy;
   using accessor_type    = _AccessorPolicy;
   using mapping_type     = typename layout_type::template mapping<extents_type>;
   using element_type     = _ElementType;
   using value_type       = remove_cv_t<element_type>;
   using index_type       = typename extents_type::index_type;
   using size_type        = typename extents_type::size_type;
   using rank_type        = typename extents_type::rank_type;
   using data_handle_type = typename accessor_type::data_handle_type;
   using reference        = typename accessor_type::reference;

   _LIBCPP_HIDE_FROM_ABI static constexpr rank_type rank() noexcept { return extents_type::rank(); }
   _LIBCPP_HIDE_FROM_ABI static constexpr rank_type rank_dynamic() noexcept { return extents_type::rank_dynamic(); }
   _LIBCPP_HIDE_FROM_ABI static constexpr size_t static_extent(rank_type __r) noexcept {
     return extents_type::static_extent(__r);
   }
   _LIBCPP_HIDE_FROM_ABI constexpr index_type extent(rank_type __r) const noexcept {
     return __map_.extents().extent(__r);
   };

 public:
   //--------------------------------------------------------------------------------
   // [mdspan.mdspan.cons], mdspan constructors, assignment, and destructor

   _LIBCPP_HIDE_FROM_ABI constexpr mdspan()
     requires((extents_type::rank_dynamic() > 0) && is_default_constructible_v<data_handle_type> &&
              is_default_constructible_v<mapping_type> && is_default_constructible_v<accessor_type>)
   = default;
   _LIBCPP_HIDE_FROM_ABI constexpr mdspan(const mdspan&) = default;
   _LIBCPP_HIDE_FROM_ABI constexpr mdspan(mdspan&&)      = default;

   template <class... _OtherIndexTypes>
     requires((is_convertible_v<_OtherIndexTypes, index_type> && ...) &&
              (is_nothrow_constructible_v<index_type, _OtherIndexTypes> && ...) &&
              ((sizeof...(_OtherIndexTypes) == rank()) || (sizeof...(_OtherIndexTypes) == rank_dynamic())) &&
              is_constructible_v<mapping_type, extents_type> && is_default_constructible_v<accessor_type>)
   _LIBCPP_HIDE_FROM_ABI explicit constexpr mdspan(data_handle_type __p, _OtherIndexTypes... __exts)
       : __ptr_(std::move(__p)), __map_(extents_type(static_cast<index_type>(std::move(__exts))...)), __acc_{} {}

   template <class _OtherIndexType, size_t _Size>
     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
              is_nothrow_constructible_v<index_type, const _OtherIndexType&> &&
              ((_Size == rank()) || (_Size == rank_dynamic())) && is_constructible_v<mapping_type, extents_type> &&
              is_default_constructible_v<accessor_type>)
   explicit(_Size != rank_dynamic())
       _LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, const array<_OtherIndexType, _Size>& __exts)
       : __ptr_(std::move(__p)), __map_(extents_type(__exts)), __acc_{} {}

   template <class _OtherIndexType, size_t _Size>
     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
              is_nothrow_constructible_v<index_type, const _OtherIndexType&> &&
              ((_Size == rank()) || (_Size == rank_dynamic())) && is_constructible_v<mapping_type, extents_type> &&
              is_default_constructible_v<accessor_type>)
   explicit(_Size != rank_dynamic())
       _LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, span<_OtherIndexType, _Size> __exts)
       : __ptr_(std::move(__p)), __map_(extents_type(__exts)), __acc_{} {}

   _LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, const extents_type& __exts)
     requires(is_default_constructible_v<accessor_type> && is_constructible_v<mapping_type, const extents_type&>)
       : __ptr_(std::move(__p)), __map_(__exts), __acc_{} {}

   _LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, const mapping_type& __m)
     requires(is_default_constructible_v<accessor_type>)
       : __ptr_(std::move(__p)), __map_(__m), __acc_{} {}

   _LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, const mapping_type& __m, const accessor_type& __a)
       : __ptr_(std::move(__p)), __map_(__m), __acc_(__a) {}

   template <class _OtherElementType, class _OtherExtents, class _OtherLayoutPolicy, class _OtherAccessor>
     requires(is_constructible_v<mapping_type, const typename _OtherLayoutPolicy::template mapping<_OtherExtents>&> &&
              is_constructible_v<accessor_type, const _OtherAccessor&>)
   explicit(!is_convertible_v<const typename _OtherLayoutPolicy::template mapping<_OtherExtents>&, mapping_type> ||
            !is_convertible_v<const _OtherAccessor&, accessor_type>)
       _LIBCPP_HIDE_FROM_ABI constexpr mdspan(
           const mdspan<_OtherElementType, _OtherExtents, _OtherLayoutPolicy, _OtherAccessor>& __other)
       : __ptr_(__other.__ptr_), __map_(__other.__map_), __acc_(__other.__acc_) {
     static_assert(is_constructible_v<data_handle_type, const typename _OtherAccessor::data_handle_type&>,
                   "mdspan: incompatible data_handle_type for mdspan construction");
     static_assert(
         is_constructible_v<extents_type, _OtherExtents>, "mdspan: incompatible extents for mdspan construction");

     // The following precondition is part of the standard, but is unlikely to be triggered.
     // The extents constructor checks this and the mapping must be storing the extents, since
     // its extents() function returns a const reference to extents_type.
     // The only way this can be triggered is if the mapping conversion constructor would for example
     // always construct its extents() only from the dynamic extents, instead of from the other extents.
     if constexpr (rank() > 0) {
       for (size_t __r = 0; __r < rank(); __r++) {
         // Not catching this could lead to out of bounds errors later
         // e.g. mdspan<int, dextents<char,1>, non_checking_layout> m =
         //        mdspan<int, dextents<unsigned, 1>, non_checking_layout>(ptr, 200); leads to an extent of -56 on m
         _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
             (static_extent(__r) == dynamic_extent) ||
                 (static_cast<index_type>(__other.extent(__r)) == static_cast<index_type>(static_extent(__r))),
             "mdspan: conversion mismatch of source dynamic extents with static extents");
       }
     }
   }

   _LIBCPP_HIDE_FROM_ABI constexpr mdspan& operator=(const mdspan&) = default;
   _LIBCPP_HIDE_FROM_ABI constexpr mdspan& operator=(mdspan&&)      = default;

   //--------------------------------------------------------------------------------
   // [mdspan.mdspan.members], members

   template <class... _OtherIndexTypes>
     requires((is_convertible_v<_OtherIndexTypes, index_type> && ...) &&
              (is_nothrow_constructible_v<index_type, _OtherIndexTypes> && ...) &&
              (sizeof...(_OtherIndexTypes) == rank()))
   _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](_OtherIndexTypes... __indices) const {
     // Note the standard layouts would also check this, but user provided ones may not, so we
     // check the precondition here
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__mdspan_detail::__is_multidimensional_index_in(extents(), __indices...),
                                         "mdspan: operator[] out of bounds access");
     return __acc_.access(__ptr_, __map_(static_cast<index_type>(std::move(__indices))...));
   }

   template <class _OtherIndexType>
     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
              is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
   _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](const array< _OtherIndexType, rank()>& __indices) const {
     return __acc_.access(__ptr_, [&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
       return __map_(__indices[_Idxs]...);
     }(make_index_sequence<rank()>()));
   }

   template <class _OtherIndexType>
     requires(is_convertible_v<const _OtherIndexType&, index_type> &&
              is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
   _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](span<_OtherIndexType, rank()> __indices) const {
     return __acc_.access(__ptr_, [&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
       return __map_(__indices[_Idxs]...);
     }(make_index_sequence<rank()>()));
   }

   _LIBCPP_HIDE_FROM_ABI constexpr size_type size() const noexcept {
     // Could leave this as only checked in debug mode: semantically size() is never
     // guaranteed to be related to any accessible range
     _LIBCPP_ASSERT_UNCATEGORIZED(
         false == ([&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
           size_type __prod = 1;
           return (__builtin_mul_overflow(__prod, extent(_Idxs), &__prod) || ... || false);
         }(make_index_sequence<rank()>())),
         "mdspan: size() is not representable as size_type");
     return [&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
       return ((static_cast<size_type>(__map_.extents().extent(_Idxs))) * ... * size_type(1));
     }(make_index_sequence<rank()>());
   }

   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool empty() const noexcept {
     return [&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
       return (rank() > 0) && ((__map_.extents().extent(_Idxs) == index_type(0)) || ... || false);
     }(make_index_sequence<rank()>());
   }

   _LIBCPP_HIDE_FROM_ABI friend constexpr void swap(mdspan& __x, mdspan& __y) noexcept {
     swap(__x.__ptr_, __y.__ptr_);
     swap(__x.__map_, __y.__map_);
     swap(__x.__acc_, __y.__acc_);
   }

   _LIBCPP_HIDE_FROM_ABI constexpr const extents_type& extents() const noexcept { return __map_.extents(); };
   _LIBCPP_HIDE_FROM_ABI constexpr const data_handle_type& data_handle() const noexcept { return __ptr_; };
   _LIBCPP_HIDE_FROM_ABI constexpr const mapping_type& mapping() const noexcept { return __map_; };
   _LIBCPP_HIDE_FROM_ABI constexpr const accessor_type& accessor() const noexcept { return __acc_; };

   // per LWG-4021 "mdspan::is_always_meow() should be noexcept"
   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_unique() noexcept { return mapping_type::is_always_unique(); };
   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_exhaustive() noexcept {
     return mapping_type::is_always_exhaustive();
   };
   _LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_strided() noexcept {
     return mapping_type::is_always_strided();
   };

   _LIBCPP_HIDE_FROM_ABI constexpr bool is_unique() const { return __map_.is_unique(); };
   _LIBCPP_HIDE_FROM_ABI constexpr bool is_exhaustive() const { return __map_.is_exhaustive(); };
   _LIBCPP_HIDE_FROM_ABI constexpr bool is_strided() const { return __map_.is_strided(); };
   _LIBCPP_HIDE_FROM_ABI constexpr index_type stride(rank_type __r) const { return __map_.stride(__r); };

 private:
   _LIBCPP_NO_UNIQUE_ADDRESS data_handle_type __ptr_{};
   _LIBCPP_NO_UNIQUE_ADDRESS mapping_type __map_{};
   _LIBCPP_NO_UNIQUE_ADDRESS accessor_type __acc_{};

   template <class, class, class, class>
   friend class mdspan;
 };

 #  if _LIBCPP_STD_VER >= 26
 template <class _ElementType, class... _OtherIndexTypes>
   requires((is_convertible_v<_OtherIndexTypes, size_t> && ...) && (sizeof...(_OtherIndexTypes) > 0))
 explicit mdspan(_ElementType*,
                 _OtherIndexTypes...) -> mdspan<_ElementType, extents<size_t, __maybe_static_ext<_OtherIndexTypes>...>>;
 #  else
 template <class _ElementType, class... _OtherIndexTypes>
   requires((is_convertible_v<_OtherIndexTypes, size_t> && ...) && (sizeof...(_OtherIndexTypes) > 0))
 explicit mdspan(_ElementType*, _OtherIndexTypes...)
     -> mdspan<_ElementType, dextents<size_t, sizeof...(_OtherIndexTypes)>>;
 #  endif

 template <class _Pointer>
   requires(is_pointer_v<remove_reference_t<_Pointer>>)
 mdspan(_Pointer&&) -> mdspan<remove_pointer_t<remove_reference_t<_Pointer>>, extents<size_t>>;

 template <class _CArray>
   requires(is_array_v<_CArray> && (rank_v<_CArray> == 1))
 mdspan(_CArray&) -> mdspan<remove_all_extents_t<_CArray>, extents<size_t, extent_v<_CArray, 0>>>;

 template <class _ElementType, class _OtherIndexType, size_t _Size>
 mdspan(_ElementType*, const array<_OtherIndexType, _Size>&) -> mdspan<_ElementType, dextents<size_t, _Size>>;

 template <class _ElementType, class _OtherIndexType, size_t _Size>
 mdspan(_ElementType*, span<_OtherIndexType, _Size>) -> mdspan<_ElementType, dextents<size_t, _Size>>;

 // This one is necessary because all the constructors take `data_handle_type`s, not
 // `_ElementType*`s, and `data_handle_type` is taken from `accessor_type::data_handle_type`, which
 // seems to throw off automatic deduction guides.
 template <class _ElementType, class _OtherIndexType, size_t... _ExtentsPack>
 mdspan(_ElementType*, const extents<_OtherIndexType, _ExtentsPack...>&)
     -> mdspan<_ElementType, extents<_OtherIndexType, _ExtentsPack...>>;

 template <class _ElementType, class _MappingType>
 mdspan(_ElementType*, const _MappingType&)
     -> mdspan<_ElementType, typename _MappingType::extents_type, typename _MappingType::layout_type>;

 template <class _MappingType, class _AccessorType>
 mdspan(const typename _AccessorType::data_handle_type, const _MappingType&, const _AccessorType&)
     -> mdspan<typename _AccessorType::element_type,
               typename _MappingType::extents_type,
               typename _MappingType::layout_type,
               _AccessorType>;

 #endif // _LIBCPP_STD_VER >= 23

 _LIBCPP_END_NAMESPACE_STD

 _LIBCPP_POP_MACROS

 #endif // _LIBCPP___MDSPAN_MDSPAN_H
	// -- C++ --
	//===----------------------------------------------------------------------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	// Kokkos v. 4.0
	// Copyright (2022) National Technology & Engineering
	// Solutions of Sandia, LLC (NTESS).
	//
	// Under the terms of Contract DE-NA0003525 with NTESS,
	// the U.S. Government retains certain rights in this software.
	//
	//===---------------------------------------------------------------------===//

	#ifndef _LIBCPP___MDSPAN_MDSPAN_H
	#define _LIBCPP___MDSPAN_MDSPAN_H

	#include <__assert>
	#include <__config>
	#include <__fwd/mdspan.h>
	#include <__mdspan/default_accessor.h>
	#include <__mdspan/extents.h>
	#include <__type_traits/extent.h>
	#include <__type_traits/is_abstract.h>
	#include <__type_traits/is_array.h>
	#include <__type_traits/is_constructible.h>
	#include <__type_traits/is_convertible.h>
	#include <__type_traits/is_nothrow_constructible.h>
	#include <__type_traits/is_pointer.h>
	#include <__type_traits/is_same.h>
	#include <__type_traits/rank.h>
	#include <__type_traits/remove_all_extents.h>
	#include <__type_traits/remove_cv.h>
	#include <__type_traits/remove_pointer.h>
	#include <__type_traits/remove_reference.h>
	#include <__utility/integer_sequence.h>
	#include <array>
	#include <cinttypes>
	#include <cstddef>
	#include <limits>
	#include <span>

	#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
	# pragma GCC system_header
	#endif

	_LIBCPP_PUSH_MACROS
	#include <__undef_macros>

	_LIBCPP_BEGIN_NAMESPACE_STD

	#if _LIBCPP_STD_VER >= 23

	// Helper for lightweight test checking that one did pass a layout policy as LayoutPolicy template argument
	namespace __mdspan_detail {
	template <class _Layout, class _Extents>
	concept __has_invalid_mapping = !requires { typename _Layout::template mapping<_Extents>; };
	} // namespace __mdspan_detail

	template <class _ElementType,
	class _Extents,
	class _LayoutPolicy = layout_right,
	class _AccessorPolicy = default_accessor<_ElementType> >
	class mdspan {
	private:
	static_assert(__mdspan_detail::__is_extents_v<_Extents>,
	"mdspan: Extents template parameter must be a specialization of extents.");
	static_assert(!is_array_v<_ElementType>, "mdspan: ElementType template parameter may not be an array type");
	static_assert(!is_abstract_v<_ElementType>, "mdspan: ElementType template parameter may not be an abstract class");
	static_assert(is_same_v<_ElementType, typename _AccessorPolicy::element_type>,
	"mdspan: ElementType template parameter must match AccessorPolicy::element_type");
	static_assert(!__mdspan_detail::__has_invalid_mapping<_LayoutPolicy, _Extents>,
	"mdspan: LayoutPolicy template parameter is invalid. A common mistake is to pass a layout mapping "
	"instead of a layout policy");

	public:
	using extents_type = _Extents;
	using layout_type = _LayoutPolicy;
	using accessor_type = _AccessorPolicy;
	using mapping_type = typename layout_type::template mapping<extents_type>;
	using element_type = _ElementType;
	using value_type = remove_cv_t<element_type>;
	using index_type = typename extents_type::index_type;
	using size_type = typename extents_type::size_type;
	using rank_type = typename extents_type::rank_type;
	using data_handle_type = typename accessor_type::data_handle_type;
	using reference = typename accessor_type::reference;

	_LIBCPP_HIDE_FROM_ABI static constexpr rank_type rank() noexcept { return extents_type::rank(); }
	_LIBCPP_HIDE_FROM_ABI static constexpr rank_type rank_dynamic() noexcept { return extents_type::rank_dynamic(); }
	_LIBCPP_HIDE_FROM_ABI static constexpr size_t static_extent(rank_type __r) noexcept {
	return extents_type::static_extent(__r);
	}
	_LIBCPP_HIDE_FROM_ABI constexpr index_type extent(rank_type __r) const noexcept {
	return __map_.extents().extent(__r);
	};

	public:
	//--------------------------------------------------------------------------------
	// [mdspan.mdspan.cons], mdspan constructors, assignment, and destructor

	_LIBCPP_HIDE_FROM_ABI constexpr mdspan()
	requires((extents_type::rank_dynamic() > 0) && is_default_constructible_v<data_handle_type> &&
	is_default_constructible_v<mapping_type> && is_default_constructible_v<accessor_type>)
	= default;
	_LIBCPP_HIDE_FROM_ABI constexpr mdspan(const mdspan&) = default;
	_LIBCPP_HIDE_FROM_ABI constexpr mdspan(mdspan&&) = default;

	template <class... _OtherIndexTypes>
	requires((is_convertible_v<_OtherIndexTypes, index_type> && ...) &&
	(is_nothrow_constructible_v<index_type, _OtherIndexTypes> && ...) &&
	((sizeof...(_OtherIndexTypes) == rank()) \|\| (sizeof...(_OtherIndexTypes) == rank_dynamic())) &&
	is_constructible_v<mapping_type, extents_type> && is_default_constructible_v<accessor_type>)
	_LIBCPP_HIDE_FROM_ABI explicit constexpr mdspan(data_handle_type __p, _OtherIndexTypes... __exts)
	: __ptr_(std::move(__p)), __map_(extents_type(static_cast<index_type>(std::move(__exts))...)), __acc_{} {}

	template <class _OtherIndexType, size_t _Size>
	requires(is_convertible_v<const _OtherIndexType&, index_type> &&
	is_nothrow_constructible_v<index_type, const _OtherIndexType&> &&
	((_Size == rank()) \|\| (_Size == rank_dynamic())) && is_constructible_v<mapping_type, extents_type> &&
	is_default_constructible_v<accessor_type>)
	explicit(_Size != rank_dynamic())
	_LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, const array<_OtherIndexType, _Size>& __exts)
	: __ptr_(std::move(__p)), __map_(extents_type(__exts)), __acc_{} {}

	template <class _OtherIndexType, size_t _Size>
	requires(is_convertible_v<const _OtherIndexType&, index_type> &&
	is_nothrow_constructible_v<index_type, const _OtherIndexType&> &&
	((_Size == rank()) \|\| (_Size == rank_dynamic())) && is_constructible_v<mapping_type, extents_type> &&
	is_default_constructible_v<accessor_type>)
	explicit(_Size != rank_dynamic())
	_LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, span<_OtherIndexType, _Size> __exts)
	: __ptr_(std::move(__p)), __map_(extents_type(__exts)), __acc_{} {}

	_LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, const extents_type& __exts)
	requires(is_default_constructible_v<accessor_type> && is_constructible_v<mapping_type, const extents_type&>)
	: __ptr_(std::move(__p)), __map_(__exts), __acc_{} {}

	_LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, const mapping_type& __m)
	requires(is_default_constructible_v<accessor_type>)
	: __ptr_(std::move(__p)), __map_(__m), __acc_{} {}

	_LIBCPP_HIDE_FROM_ABI constexpr mdspan(data_handle_type __p, const mapping_type& __m, const accessor_type& __a)
	: __ptr_(std::move(__p)), __map_(__m), __acc_(__a) {}

	template <class _OtherElementType, class _OtherExtents, class _OtherLayoutPolicy, class _OtherAccessor>
	requires(is_constructible_v<mapping_type, const typename _OtherLayoutPolicy::template mapping<_OtherExtents>&> &&
	is_constructible_v<accessor_type, const _OtherAccessor&>)
	explicit(!is_convertible_v<const typename _OtherLayoutPolicy::template mapping<_OtherExtents>&, mapping_type> \|\|
	!is_convertible_v<const _OtherAccessor&, accessor_type>)
	_LIBCPP_HIDE_FROM_ABI constexpr mdspan(
	const mdspan<_OtherElementType, _OtherExtents, _OtherLayoutPolicy, _OtherAccessor>& __other)
	: __ptr_(__other.__ptr_), __map_(__other.__map_), __acc_(__other.__acc_) {
	static_assert(is_constructible_v<data_handle_type, const typename _OtherAccessor::data_handle_type&>,
	"mdspan: incompatible data_handle_type for mdspan construction");
	static_assert(
	is_constructible_v<extents_type, _OtherExtents>, "mdspan: incompatible extents for mdspan construction");

	// The following precondition is part of the standard, but is unlikely to be triggered.
	// The extents constructor checks this and the mapping must be storing the extents, since
	// its extents() function returns a const reference to extents_type.
	// The only way this can be triggered is if the mapping conversion constructor would for example
	// always construct its extents() only from the dynamic extents, instead of from the other extents.
	if constexpr (rank() > 0) {
	for (size_t __r = 0; __r < rank(); __r++) {
	// Not catching this could lead to out of bounds errors later
	// e.g. mdspan<int, dextents<char,1>, non_checking_layout> m =
	// mdspan<int, dextents<unsigned, 1>, non_checking_layout>(ptr, 200); leads to an extent of -56 on m
	_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
	(static_extent(__r) == dynamic_extent) \|\|
	(static_cast<index_type>(__other.extent(__r)) == static_cast<index_type>(static_extent(__r))),
	"mdspan: conversion mismatch of source dynamic extents with static extents");
	}
	}
	}

	_LIBCPP_HIDE_FROM_ABI constexpr mdspan& operator=(const mdspan&) = default;
	_LIBCPP_HIDE_FROM_ABI constexpr mdspan& operator=(mdspan&&) = default;

	//--------------------------------------------------------------------------------
	// [mdspan.mdspan.members], members

	template <class... _OtherIndexTypes>
	requires((is_convertible_v<_OtherIndexTypes, index_type> && ...) &&
	(is_nothrow_constructible_v<index_type, _OtherIndexTypes> && ...) &&
	(sizeof...(_OtherIndexTypes) == rank()))
	_LIBCPP_HIDE_FROM_ABI constexpr reference operator[](_OtherIndexTypes... __indices) const {
	// Note the standard layouts would also check this, but user provided ones may not, so we
	// check the precondition here
	_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__mdspan_detail::__is_multidimensional_index_in(extents(), __indices...),
	"mdspan: operator[] out of bounds access");
	return __acc_.access(__ptr_, __map_(static_cast<index_type>(std::move(__indices))...));
	}

	template <class _OtherIndexType>
	requires(is_convertible_v<const _OtherIndexType&, index_type> &&
	is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
	_LIBCPP_HIDE_FROM_ABI constexpr reference operator[](const array< _OtherIndexType, rank()>& __indices) const {
	return __acc_.access(__ptr_, [&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
	return __map_(__indices[_Idxs]...);
	}(make_index_sequence<rank()>()));
	}

	template <class _OtherIndexType>
	requires(is_convertible_v<const _OtherIndexType&, index_type> &&
	is_nothrow_constructible_v<index_type, const _OtherIndexType&>)
	_LIBCPP_HIDE_FROM_ABI constexpr reference operator[](span<_OtherIndexType, rank()> __indices) const {
	return __acc_.access(__ptr_, [&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
	return __map_(__indices[_Idxs]...);
	}(make_index_sequence<rank()>()));
	}

	_LIBCPP_HIDE_FROM_ABI constexpr size_type size() const noexcept {
	// Could leave this as only checked in debug mode: semantically size() is never
	// guaranteed to be related to any accessible range
	_LIBCPP_ASSERT_UNCATEGORIZED(
	false == ([&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
	size_type __prod = 1;
	return (__builtin_mul_overflow(__prod, extent(_Idxs), &__prod) \|\| ... \|\| false);
	}(make_index_sequence<rank()>())),
	"mdspan: size() is not representable as size_type");
	return [&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
	return ((static_cast<size_type>(__map_.extents().extent(_Idxs))) * ... * size_type(1));
	}(make_index_sequence<rank()>());
	}

	[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool empty() const noexcept {
	return [&]<size_t... _Idxs>(index_sequence<_Idxs...>) {
	return (rank() > 0) && ((__map_.extents().extent(_Idxs) == index_type(0)) \|\| ... \|\| false);
	}(make_index_sequence<rank()>());
	}

	_LIBCPP_HIDE_FROM_ABI friend constexpr void swap(mdspan& __x, mdspan& __y) noexcept {
	swap(__x.__ptr_, __y.__ptr_);
	swap(__x.__map_, __y.__map_);
	swap(__x.__acc_, __y.__acc_);
	}

	_LIBCPP_HIDE_FROM_ABI constexpr const extents_type& extents() const noexcept { return __map_.extents(); };
	_LIBCPP_HIDE_FROM_ABI constexpr const data_handle_type& data_handle() const noexcept { return __ptr_; };
	_LIBCPP_HIDE_FROM_ABI constexpr const mapping_type& mapping() const noexcept { return __map_; };
	_LIBCPP_HIDE_FROM_ABI constexpr const accessor_type& accessor() const noexcept { return __acc_; };

	// per LWG-4021 "mdspan::is_always_meow() should be noexcept"
	_LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_unique() noexcept { return mapping_type::is_always_unique(); };
	_LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_exhaustive() noexcept {
	return mapping_type::is_always_exhaustive();
	};
	_LIBCPP_HIDE_FROM_ABI static constexpr bool is_always_strided() noexcept {
	return mapping_type::is_always_strided();
	};

	_LIBCPP_HIDE_FROM_ABI constexpr bool is_unique() const { return __map_.is_unique(); };
	_LIBCPP_HIDE_FROM_ABI constexpr bool is_exhaustive() const { return __map_.is_exhaustive(); };
	_LIBCPP_HIDE_FROM_ABI constexpr bool is_strided() const { return __map_.is_strided(); };
	_LIBCPP_HIDE_FROM_ABI constexpr index_type stride(rank_type __r) const { return __map_.stride(__r); };

	private:
	_LIBCPP_NO_UNIQUE_ADDRESS data_handle_type __ptr_{};
	_LIBCPP_NO_UNIQUE_ADDRESS mapping_type __map_{};
	_LIBCPP_NO_UNIQUE_ADDRESS accessor_type __acc_{};

	template <class, class, class, class>
	friend class mdspan;
	};

	# if _LIBCPP_STD_VER >= 26
	template <class _ElementType, class... _OtherIndexTypes>
	requires((is_convertible_v<_OtherIndexTypes, size_t> && ...) && (sizeof...(_OtherIndexTypes) > 0))
	explicit mdspan(_ElementType*,
	_OtherIndexTypes...) -> mdspan<_ElementType, extents<size_t, __maybe_static_ext<_OtherIndexTypes>...>>;
	# else
	template <class _ElementType, class... _OtherIndexTypes>
	requires((is_convertible_v<_OtherIndexTypes, size_t> && ...) && (sizeof...(_OtherIndexTypes) > 0))
	explicit mdspan(_ElementType*, _OtherIndexTypes...)
	-> mdspan<_ElementType, dextents<size_t, sizeof...(_OtherIndexTypes)>>;
	# endif

	template <class _Pointer>
	requires(is_pointer_v<remove_reference_t<_Pointer>>)
	mdspan(_Pointer&&) -> mdspan<remove_pointer_t<remove_reference_t<_Pointer>>, extents<size_t>>;

	template <class _CArray>
	requires(is_array_v<_CArray> && (rank_v<_CArray> == 1))
	mdspan(_CArray&) -> mdspan<remove_all_extents_t<_CArray>, extents<size_t, extent_v<_CArray, 0>>>;

	template <class _ElementType, class _OtherIndexType, size_t _Size>
	mdspan(_ElementType*, const array<_OtherIndexType, _Size>&) -> mdspan<_ElementType, dextents<size_t, _Size>>;

	template <class _ElementType, class _OtherIndexType, size_t _Size>
	mdspan(_ElementType*, span<_OtherIndexType, _Size>) -> mdspan<_ElementType, dextents<size_t, _Size>>;

	// This one is necessary because all the constructors take `data_handle_type`s, not
	// `_ElementType*`s, and `data_handle_type` is taken from `accessor_type::data_handle_type`, which
	// seems to throw off automatic deduction guides.
	template <class _ElementType, class _OtherIndexType, size_t... _ExtentsPack>
	mdspan(_ElementType*, const extents<_OtherIndexType, _ExtentsPack...>&)
	-> mdspan<_ElementType, extents<_OtherIndexType, _ExtentsPack...>>;

	template <class _ElementType, class _MappingType>
	mdspan(_ElementType*, const _MappingType&)
	-> mdspan<_ElementType, typename _MappingType::extents_type, typename _MappingType::layout_type>;

	template <class _MappingType, class _AccessorType>
	mdspan(const typename _AccessorType::data_handle_type, const _MappingType&, const _AccessorType&)
	-> mdspan<typename _AccessorType::element_type,
	typename _MappingType::extents_type,
	typename _MappingType::layout_type,
	_AccessorType>;

	#endif // _LIBCPP_STD_VER >= 23

	_LIBCPP_END_NAMESPACE_STD

	_LIBCPP_POP_MACROS

	#endif // _LIBCPP___MDSPAN_MDSPAN_H