Few initial comments. I will do a full-review with checks against wording
later today or tomorrow.
On Fri, Jun 27, 2025 at 11:37 AM Luc Grosheintz <luc.groshei...@gmail.com>
wrote:
> Implements the class mdspan as described in N4950, i.e. without P3029.
> It also adds tests for mdspan.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/mdspan (mdspan): New class.
> * src/c++23/std.cc.in: Add std::mdspan.
> * testsuite/23_containers/mdspan/class_mandate_neg.cc: New test.
> * testsuite/23_containers/mdspan/mdspan.cc: New test.
> * testsuite/23_containers/mdspan/layout_like.h: Add class
> LayoutLike which models a user-defined layout.
>
> Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
> ---
> libstdc++-v3/include/std/mdspan | 282 +++++++++
> libstdc++-v3/src/c++23/std.cc.in | 3 +-
> .../23_containers/mdspan/class_mandate_neg.cc | 58 ++
> .../23_containers/mdspan/layout_like.h | 63 ++
> .../testsuite/23_containers/mdspan/mdspan.cc | 540 ++++++++++++++++++
> 5 files changed, 945 insertions(+), 1 deletion(-)
> create mode 100644
> libstdc++-v3/testsuite/23_containers/mdspan/class_mandate_neg.cc
> create mode 100644
> libstdc++-v3/testsuite/23_containers/mdspan/layout_like.h
> create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
>
> diff --git a/libstdc++-v3/include/std/mdspan
> b/libstdc++-v3/include/std/mdspan
> index e198d65bba3..852f881971e 100644
> --- a/libstdc++-v3/include/std/mdspan
> +++ b/libstdc++-v3/include/std/mdspan
> @@ -1052,6 +1052,288 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { return __p + __i; }
> };
>
> + namespace __mdspan
> + {
> + template<typename _Extents, typename _IndexType, size_t _Nm>
> + constexpr bool
> + __is_multi_index(const _Extents& __exts, span<_IndexType, _Nm>
> __indices)
> + {
> + static_assert(__exts.rank() == _Nm);
> + for (size_t __i = 0; __i < __exts.rank(); ++__i)
> + if (__indices[__i] >= __exts.extent(__i))
> + return false;
> + return true;
> + }
> + }
> +
> + template<typename _ElementType, typename _Extents,
> + typename _LayoutPolicy = layout_right,
> + typename _AccessorPolicy = default_accessor<_ElementType>>
> + class mdspan
> + {
> + static_assert(!is_array_v<_ElementType>,
> + "ElementType must not be an array type");
> + static_assert(!is_abstract_v<_ElementType>,
> + "ElementType must not be an abstract class type");
> + static_assert(__mdspan::__is_extents<_Extents>,
> + "Extents must be a specialization of std::extents");
> + static_assert(is_same_v<_ElementType,
> + typename _AccessorPolicy::element_type>);
> +
> + 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;
> +
> + static constexpr rank_type
> + rank() noexcept { return extents_type::rank(); }
> +
> + static constexpr rank_type
> + rank_dynamic() noexcept { return extents_type::rank_dynamic(); }
> +
> + static constexpr size_t
> + static_extent(rank_type __r) noexcept
> + { return extents_type::static_extent(__r); }
> +
> + constexpr index_type
> + extent(rank_type __r) const noexcept { return
> extents().extent(__r); }
> +
> + constexpr
> + mdspan()
> + requires (rank_dynamic() > 0 &&
> + is_default_constructible_v<data_handle_type> &&
> + is_default_constructible_v<mapping_type> &&
> + is_default_constructible_v<accessor_type>)
> + : _M_accessor{}, _M_mapping{}, _M_handle{}
> + { }
> +
> + constexpr
> + mdspan(const mdspan& __other) = default;
> +
> + constexpr
> + mdspan(mdspan&& __other) = default;
> +
> + template<__mdspan::__valid_index_type<index_type>... _OIndexTypes>
> + requires ((sizeof...(_OIndexTypes) == rank()
> + || sizeof...(_OIndexTypes) == rank_dynamic())
> + && is_constructible_v<mapping_type, extents_type>
> + && is_default_constructible_v<accessor_type>)
> + constexpr explicit
> + mdspan(data_handle_type __handle, _OIndexTypes... __exts)
> + : _M_accessor{},
> +
> _M_mapping(_Extents(static_cast<index_type>(std::move(__exts))...)),
> + _M_handle(std::move(__handle))
> + { }
> +
> + template<__mdspan::__valid_index_type<index_type> _OIndexType,
> + size_t _Nm>
> + requires ((_Nm == rank() || _Nm == rank_dynamic())
> + && is_constructible_v<mapping_type, extents_type>
> + && is_default_constructible_v<accessor_type>)
> + constexpr explicit(_Nm != rank_dynamic())
> + mdspan(data_handle_type __handle, span<_OIndexType, _Nm> __exts)
> + : _M_accessor{}, _M_mapping(extents_type(__exts)),
> + _M_handle(std::move(__handle))
> + { }
> +
> + template<__mdspan::__valid_index_type<index_type> _OIndexType,
> + size_t _Nm>
> + requires ((_Nm == rank() || _Nm == rank_dynamic())
> + && is_constructible_v<mapping_type, extents_type>
> + && is_default_constructible_v<accessor_type>)
> + constexpr explicit(_Nm != rank_dynamic())
> + mdspan(data_handle_type __handle, const array<_OIndexType, _Nm>&
> __exts)
> + : _M_accessor{}, _M_mapping(extents_type(__exts)),
> + _M_handle(std::move(__handle))
> + { }
> +
> + constexpr
> + mdspan(data_handle_type __handle, const extents_type& __exts)
> + requires (is_constructible_v<mapping_type, const extents_type&>
> + && is_default_constructible_v<accessor_type>)
> + : _M_accessor{}, _M_mapping(__exts), _M_handle(std::move(__handle))
> + { }
> +
> + constexpr
> + mdspan(data_handle_type __handle, const mapping_type& __mapping)
> + requires (is_default_constructible_v<accessor_type>)
> + : _M_accessor{}, _M_mapping(__mapping),
> _M_handle(std::move(__handle))
> + { }
> +
> + constexpr
> + mdspan(data_handle_type __handle, const mapping_type& __mapping,
> + const accessor_type& __accessor)
> + : _M_accessor(__accessor), _M_mapping(__mapping),
> + _M_handle(std::move(__handle))
> + { }
> +
> + template<typename _OElementType, typename _OExtents, typename
> _OLayout,
> + typename _OAccessor>
> + requires (is_constructible_v<mapping_type,
> + const typename _OLayout::mapping<_OExtents>&>
> + && is_constructible_v<accessor_type, const _OAccessor&>)
> + constexpr explicit(!(is_convertible_v<
> + const typename _OLayout::mapping<_OExtents>&, mapping_type>
> + && is_convertible_v<const _OAccessor&, accessor_type>))
> + mdspan(const mdspan<_OElementType, _OExtents, _OLayout,
> _OAccessor>&
> + __other)
> + : _M_accessor(__other.accessor()), _M_mapping(__other.mapping()),
> + _M_handle(__other.data_handle())
> + {
> + static_assert(is_constructible_v<data_handle_type,
> + const typename _OAccessor::data_handle_type&>);
> + static_assert(is_constructible_v<extents_type, _OExtents>);
> + }
> +
> + constexpr mdspan&
> + operator=(const mdspan& __other) = default;
> +
> + constexpr mdspan&
> + operator=(mdspan&& __other) = default;
> +
> + template<__mdspan::__valid_index_type<index_type>... _OIndexTypes>
> + requires (sizeof...(_OIndexTypes) == rank())
> + constexpr reference
> + operator[](_OIndexTypes... __indices) const
> + {
> + auto __checked_call = [this](auto... __idxs) -> index_type
> + {
> + if constexpr
> (!__mdspan::__standardized_mapping<mapping_type>)
>
As mentioned in e-mail for PATCH 1/5, I would always place a check here.
> + __glibcxx_assert(__mdspan::__is_multi_index(extents(),
> + span<const index_type, sizeof...(__idxs)>({__idxs...})));
> + return _M_mapping(__idxs...);
> + };
> +
> + auto __index = __checked_call(
> + static_cast<index_type>(std::move(__indices))...);
> + return _M_accessor.access(_M_handle, __index);
> + }
> +
> + template<__mdspan::__valid_index_type<index_type> _OIndexType>
> + constexpr reference
> + operator[](span<_OIndexType, rank()> __indices) const
> + {
> + auto __call = [&]<size_t... _Counts>(index_sequence<_Counts...>)
> + -> reference
> + { return (*this)[index_type(as_const(__indices[_Counts]))...];
> };
> + return __call(make_index_sequence<rank()>());
> + }
> +
> + template<__mdspan::__valid_index_type<index_type> _OIndexType>
> + constexpr reference
> + operator[](const array<_OIndexType, rank()>& __indices) const
> + { return (*this)[span<const _OIndexType, rank()>(__indices)]; }
> +
> + constexpr size_type
> + size() const noexcept
> + {
> + __glibcxx_assert(cmp_less_equal(_M_mapping.required_span_size(),
> + numeric_limits<size_t>::max()));
> + return size_type(__mdspan::__fwd_prod(extents(), rank()));
> + }
> +
> + [[nodiscard]] constexpr bool
> + empty() const noexcept
> + {
> + return __mdspan::__empty(extents());
> + }
> +
> + friend constexpr void
> + swap(mdspan& __x, mdspan& __y) noexcept
> + {
> + std::swap(__x._M_mapping, __y._M_mapping);
> + std::swap(__x._M_accessor, __y._M_accessor);
> + std::swap(__x._M_handle, __y._M_handle);
> + }
> +
> + constexpr const extents_type&
> + extents() const noexcept { return _M_mapping.extents(); }
> +
> + constexpr const data_handle_type&
> + data_handle() const noexcept { return _M_handle; }
> +
> + constexpr const mapping_type&
> + mapping() const noexcept { return _M_mapping; }
> +
> + constexpr const accessor_type&
> + accessor() const noexcept { return _M_accessor; }
> +
> + static constexpr bool
> + is_always_unique() { return mapping_type::is_always_unique(); }
> +
> + static constexpr bool
> + is_always_exhaustive() { return
> mapping_type::is_always_exhaustive(); }
> +
> + static constexpr bool
> + is_always_strided() { return mapping_type::is_always_strided(); }
> +
> + constexpr bool
> + is_unique() const { return _M_mapping.is_unique(); }
> +
> + constexpr bool
> + is_exhaustive() const { return _M_mapping.is_exhaustive(); }
> +
> + constexpr bool
> + is_strided() const { return _M_mapping. is_strided(); }
> +
> + constexpr index_type
> + stride(rank_type __r) const { return _M_mapping.stride(__r); }
> +
> + private:
> + [[no_unique_address]] accessor_type _M_accessor;
> + [[no_unique_address]] mapping_type _M_mapping;
> + [[no_unique_address]] data_handle_type _M_handle;
> + };
> +
> + template<typename _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<typename _Pointer>
> + requires(is_pointer_v<remove_reference_t<_Pointer>>)
> + mdspan(_Pointer&&)
> + -> mdspan<remove_pointer_t<remove_reference_t<_Pointer>>,
> extents<size_t>>;
> +
> + template<typename _ElementType, typename... _Integrals>
> + requires((is_convertible_v<_Integrals, size_t> && ...)
> + && sizeof...(_Integrals) > 0)
> + explicit mdspan(_ElementType*, _Integrals...)
> + -> mdspan<_ElementType, dextents<size_t, sizeof...(_Integrals)>>;
>
We could use __mdspan::__dynamic_extent<Integrals>... here instead of
computing dextents.
This would make implementation of P3029R1 simpler.
> +
> + template<typename _ElementType, typename _OIndexType, size_t _Nm>
> + mdspan(_ElementType*, span<_OIndexType, _Nm>)
> + -> mdspan<_ElementType, dextents<size_t, _Nm>>;
> +
> + template<typename _ElementType, typename _OIndexType, size_t _Nm>
> + mdspan(_ElementType*, const array<_OIndexType, _Nm>&)
> + -> mdspan<_ElementType, dextents<size_t, _Nm>>;
> +
> + template<typename _ElementType, typename _IndexType, size_t...
> _ExtentsPack>
> + mdspan(_ElementType*, const extents<_IndexType, _ExtentsPack...>&)
> + -> mdspan<_ElementType, extents<_IndexType, _ExtentsPack...>>;
> +
> + template<typename _ElementType, typename _MappingType>
> + mdspan(_ElementType*, const _MappingType&)
> + -> mdspan<_ElementType, typename _MappingType::extents_type,
> + typename _MappingType::layout_type>;
> +
> + template<typename _MappingType, typename _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>;
> +
> _GLIBCXX_END_NAMESPACE_VERSION
> }
> #endif
> diff --git a/libstdc++-v3/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/
> std.cc.in
> index e692caaa5f9..b62114be467 100644
> --- a/libstdc++-v3/src/c++23/std.cc.in
> +++ b/libstdc++-v3/src/c++23/std.cc.in
> @@ -1851,7 +1851,8 @@ export namespace std
> using std::layout_right;
> using std::layout_stride;
> using std::default_accessor;
> - // FIXME layout_left_padded, layout_right_padded, aligned_accessor and
> mdspan
> + using std::mdspan;
> + // FIXME layout_left_padded, layout_right_padded, aligned_accessor,
> mdsubspan
> }
> #endif
>
> diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/class_mandate_neg.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/class_mandate_neg.cc
> new file mode 100644
> index 00000000000..96b9a2c41bb
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/class_mandate_neg.cc
> @@ -0,0 +1,58 @@
> +// { dg-do compile { target c++23 } }
> +#include<mdspan>
> +
> +#include <cstdint>
> +#include "layout_like.h"
> +
> +struct ExtentsLike
> +{
> + using index_type = int;
> + using size_type = unsigned int;
> + using rank_type = size_t;
> +
> + static constexpr size_t rank() { return 1; }
> + static constexpr size_t rank_dynamic() { return 0; }
> +};
> +
> +constexpr bool
> +test_custom_extents_type()
> +{
> + std::mdspan<double, ExtentsLike> md1; // { dg-error "required from
> here" }
> + return true;
> +}
> +static_assert(test_custom_extents_type());
> +
> +constexpr bool
> +test_element_type_mismatch()
> +{
> + using E = std::extents<int, 1>;
> + using L = std::layout_right;
> + using A = std::default_accessor<double>;
> +
> + [[maybe_unused]] std::mdspan<float, E, L, A> md2; // { dg-error
> "required from here" }
> + return true;
> +};
> +static_assert(test_element_type_mismatch());
> +
> +template<typename Layout>
> +constexpr bool
> +test_invalid_multi_index()
>
I think I would put this test in separate file, like out_of_bound_neg.cc.
> +{
> +
> + double data = 1.1;
> + auto m = typename Layout::mapping<std::extents<int, 1, 2, 3>>{};
> + auto md = std::mdspan(&data, m);
> +
> + [[maybe_unused]] double x = md[0, 2, 2]; // { dg-error "expansion of" }
> + return true;
> +};
> +static_assert(test_invalid_multi_index<LayoutLike>()); // { dg-error
> "expansion of" }
> +static_assert(test_invalid_multi_index<std::layout_left>()); // {
> dg-error "expansion of" }
> +static_assert(test_invalid_multi_index<std::layout_right>()); // {
> dg-error "expansion of" }
> +static_assert(test_invalid_multi_index<std::layout_stride>()); // {
> dg-error "expansion of" }
> +
> +// { dg-prune-output "Extents must be a specialization of std::extents" }
> +// { dg-prune-output "no type named '_S_storage'" }
> +// { dg-prune-output "non-constant condition" }
> +// { dg-prune-output "static assertion failed" }
> +// { dg-prune-output "__glibcxx_assert" }
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/layout_like.h
> b/libstdc++-v3/testsuite/23_containers/mdspan/layout_like.h
> new file mode 100644
> index 00000000000..17ccf52c6a6
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/layout_like.h
> @@ -0,0 +1,63 @@
> +#pragma once
> +
> +struct LayoutLike
> +{
> + template<typename Extents>
> + class mapping
> + {
> + public:
> + using extents_type = Extents;
> + 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 layout_type = LayoutLike;
> +
> + constexpr
> + mapping() noexcept = default;
> +
> + constexpr
> + mapping(Extents exts)
> + : m_exts(exts)
> + { }
> +
> + constexpr const extents_type&
> + extents() const noexcept { return m_exts; }
> +
> + constexpr index_type
> + required_span_size() const noexcept
> + { return 1; }
> +
> + template<typename... Indices>
> + requires (sizeof...(Indices) == extents_type::rank())
> + constexpr index_type
> + operator()(Indices...) const noexcept
> + { return 0; }
> +
> + static constexpr bool
> + is_always_unique() noexcept
> + { return false; }
> +
> + static constexpr bool
> + is_always_exhaustive() noexcept
> + { return false; }
> +
> + static constexpr bool
> + is_always_strided() noexcept
> + { return false; }
> +
> + static constexpr bool
> + is_unique() noexcept
> + { return false; }
> +
> + static constexpr bool
> + is_exhaustive() noexcept
> + { return false; }
> +
> + static constexpr bool
> + is_strided() noexcept
> + { return false; }
> +
> + private:
> + Extents m_exts;
> + };
> +};
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> new file mode 100644
> index 00000000000..d2672878d69
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> @@ -0,0 +1,540 @@
> +// { dg-do run { target c++23 } }
> +#include <mdspan>
> +
> +#include <testsuite_hooks.h>
> +#include "extents/int_like.h"
> +#include "layout_like.h"
> +
> +constexpr auto dyn = std::dynamic_extent;
> +
> +template<typename MDSpan, typename T, typename E, typename L =
> std::layout_right,
> + typename A = std::default_accessor<T>>
> + constexpr void
> + assert_typedefs()
> + {
> + static_assert(std::same_as<typename MDSpan::extents_type, E>);
> + static_assert(std::same_as<typename MDSpan::layout_type, L>);
> + static_assert(std::same_as<typename MDSpan::accessor_type, A>);
> + static_assert(std::same_as<typename MDSpan::mapping_type,
> + typename L::mapping<E>>);
> + static_assert(std::same_as<typename MDSpan::element_type, T>);
> + static_assert(std::same_as<typename MDSpan::value_type,
> + std::remove_const_t<T>>);
> + static_assert(std::same_as<typename MDSpan::index_type,
> + typename E::index_type>);
> + static_assert(std::same_as<typename MDSpan::size_type,
> + typename E::size_type>);
> + static_assert(std::same_as<typename MDSpan::rank_type,
> + typename E::rank_type>);
> + static_assert(std::same_as<typename MDSpan::data_handle_type,
> + typename A::data_handle_type>);
> + static_assert(std::same_as<typename MDSpan::reference,
> + typename A::reference>);
> + }
> +
> +template<typename T, typename E, typename L, template<typename U>
> typename A>
> + constexpr void
> + test_typedefs()
> + { assert_typedefs<std::mdspan<T, E, L, A<T>>, T, E, L, A<T>>(); }
> +
> +constexpr void
> +test_typedefs_all()
> +{
> + using E = std::extents<int, 1, 2>;
> + using L = std::layout_left;
> +
> + test_typedefs<double, E, L, std::default_accessor>();
> + test_typedefs<const double, E, L, std::default_accessor>();
> +}
> +
> +template<typename MDSpan>
> + constexpr void
> + test_rank()
> + {
> + using Extents = typename MDSpan::extents_type;
> + static_assert(MDSpan::rank() == Extents::rank());
> + static_assert(MDSpan::rank_dynamic() == Extents::rank_dynamic());
> + }
> +
> +constexpr bool
> +test_rank_all()
> +{
> + test_rank<std::mdspan<double, std::extents<int>>>();
> + test_rank<std::mdspan<double, std::extents<int, 1>>>();
> + test_rank<std::mdspan<double, std::extents<int, dyn>>>();
> + return true;
> +}
> +
> +template<typename Extents>
> + constexpr void
> + test_extent(Extents exts)
> + {
> + double data = 1.0;
> + auto md = std::mdspan(&data, exts);
> + using MDSpan = decltype(md);
> +
> + for(size_t i = 0; i < MDSpan::rank(); ++i)
> + {
> + VERIFY(MDSpan::static_extent(i) == Extents::static_extent(i));
> + VERIFY(md.extent(i) == exts.extent(i));
> + }
> + }
> +
> +constexpr bool
> +test_extent_all()
> +{
> + // For rank == 0, check existence of the methods without calling them.
> + test_extent(std::extents<int>{});
> + test_extent(std::extents<int, 0>{});
> + test_extent(std::extents<int, dyn>{});
> + return true;
> +}
> +
> +template<typename MDSpan>
> + constexpr void
> + test_class_properties()
> + {
> + static_assert(std::copyable<MDSpan>);
> + static_assert(std::is_nothrow_move_constructible_v<MDSpan>);
> + static_assert(std::is_nothrow_move_assignable_v<MDSpan>);
> + static_assert(std::is_nothrow_swappable_v<MDSpan>);
> + constexpr bool trivially_copyable =
> + std::is_trivially_copyable_v<typename MDSpan::accessor_type>
> + && std::is_trivially_copyable_v<typename MDSpan::mapping_type>
> + && std::is_trivially_copyable_v<typename MDSpan::data_handle_type>;
> + static_assert(std::is_trivially_copyable_v<MDSpan> ==
> trivially_copyable);
> + }
> +
> +constexpr bool
> +test_class_properties_all()
> +{
> + test_class_properties<std::mdspan<double, std::extents<int>>>();
> + test_class_properties<std::mdspan<double, std::extents<int, 1>>>();
> + test_class_properties<std::mdspan<double, std::extents<int, dyn>>>();
> + return true;
> +}
> +
> +constexpr bool
> +test_default_ctor()
> +{
> + static_assert(!std::is_default_constructible_v<std::mdspan<double,
> + std::extents<int>>>);
> + static_assert(!std::is_default_constructible_v<std::mdspan<double,
> + std::extents<int, 1>>>);
> + static_assert(std::is_default_constructible_v<std::mdspan<double,
> + std::extents<int, dyn>>>);
> +
> + std::mdspan<double, std::extents<int, dyn>> md;
> + VERIFY(md.data_handle() == nullptr);
> + VERIFY(md.extent(0) == 0);
> + return true;
> +}
> +
> +constexpr bool
> +test_from_other()
> +{
> + using Extents = std::extents<int, 3, 5, 7>;
> + auto exts = Extents{};
> +
> + auto mapping = std::layout_right::mapping(exts);
> + constexpr size_t n = mapping.required_span_size();
> + std::array<double, n> storage{};
> +
> + auto md1 = std::mdspan(storage.data(), exts);
> + auto md2 = std::mdspan<double, std::dextents<int, 3>>(md1);
> +
> + VERIFY(md1.data_handle() == md2.data_handle());
> + VERIFY(md1.size() == md2.size());
> +
> + static_assert(!std::is_convertible_v<
> + std::mdspan<double, std::extents<unsigned int, 2>>,
> + std::mdspan<double, std::extents<int, 2>>>);
> +
> + return true;
> +}
> +
> +template<typename T, typename E, typename L = std::layout_right,
> + typename A = std::default_accessor<T>>
> + constexpr void
> + assert_deduced_typedefs(auto md)
> + { assert_typedefs<decltype(md), T, E, L, A>(); }
> +
> +constexpr bool
> +test_from_carray()
> +{
> + constexpr size_t n = 5;
> + double data[n] = {1.1, 2.2, 3.3, 4.4, 5.5};
> +
> + auto md = std::mdspan(data);
> + assert_deduced_typedefs<double, std::extents<size_t, n>>(md);
> + VERIFY(md.rank() == 1);
> + VERIFY(md.rank_dynamic() == 0);
> + VERIFY(md[2] == data[2]);
> + return true;
> +}
> +
> +constexpr bool
> +test_from_pointer()
> +{
> + double value = 12.3;
> + auto md = std::mdspan(&value);
> + assert_deduced_typedefs<double, std::extents<size_t>>(md);
> + VERIFY(md.rank() == 0);
> + VERIFY(md.rank_dynamic() == 0);
> + VERIFY(md[] == value);
> + return true;
> +}
> +
> +constexpr bool
> +test_from_pointer_and_shape()
> +{
> + constexpr size_t n = 6;
> + std::array<double, n> data{1.1, 2.2, 3.3, 4.4, 5.5, 6.6};
> + std::array<int, 2> shape{2, 3};
> + std::span<const int, 2> shape_view(shape);
> +
> + auto verify = [&data](auto md)
> + {
> + assert_deduced_typedefs<double, std::dextents<size_t, 2>>(md);
> + VERIFY(md.rank() == 2);
> + VERIFY(md.rank_dynamic() == 2);
> + VERIFY((md[0, 0]) == data[0]);
> + VERIFY((md[0, 1]) == data[1]);
> + VERIFY((md[1, 0]) == data[3]);
> + };
> +
> + verify(std::mdspan(data.data(), shape[0], shape[1]));
> + verify(std::mdspan(data.data(), shape));
> + verify(std::mdspan(data.data(), shape_view));
> +
> + std::mdspan<double, std::dextents<size_t, 2>> md1 = {data.data(),
> shape};
> + verify(md1);
> +
> + std::mdspan<double, std::dextents<size_t, 2>> md2 = {data.data(),
> shape_view};
> + verify(md2);
> +
> + static_assert(std::is_constructible_v<
> + std::mdspan<float, std::extents<int, 3, 5>>, float*>);
> + static_assert(!std::is_constructible_v<
> + std::mdspan<float, std::extents<int, 3, 5>>, float*, int>);
> + static_assert(std::is_constructible_v<
> + std::mdspan<float, std::extents<int, 3, 5>>, float*, int, int>);
> + static_assert(std::is_constructible_v<
> + std::mdspan<float, std::extents<int, 3, 5>>, float*, std::span<int,
> 0>>);
> + static_assert(std::is_constructible_v<
> + std::mdspan<float, std::extents<int, 3, 5>>, float*, std::span<int,
> 2>>);
> + static_assert(!std::is_convertible_v<
> + float*, std::mdspan<float, std::extents<int, 3, 5>>>);
> +
> + static_assert(std::is_constructible_v<
> + std::mdspan<float, std::dextents<int, 2>>, float*, std::span<int,
> 2>>);
> + static_assert(!std::is_constructible_v<
> + std::mdspan<float, std::dextents<int, 2>>, float*, std::span<int,
> dyn>>);
> + return true;
> +}
> +
> +constexpr bool
> +test_from_extents()
> +{
> + constexpr size_t n = 3*5*7;
> + std::array<double, n> storage{};
> + using Extents = std::extents<int, 3, 5, 7>;
> + auto exts = Extents{};
> + auto md = std::mdspan(storage.data(), exts);
> +
> + assert_deduced_typedefs<double, Extents>(md);
> + VERIFY(md.data_handle() == storage.data());
> + VERIFY(md.extents() == exts);
> + return true;
> +}
> +
> +constexpr bool
> +test_from_mapping()
> +{
> + constexpr size_t n = 3*5*7;
> + std::array<double, n> storage{};
> + using Extents = std::extents<int, 3, 5, 7>;
> +
> + auto exts = Extents{};
> + auto m = std::layout_left::mapping(exts);
> + auto md = std::mdspan(storage.data(), m);
> +
> + assert_deduced_typedefs<double, Extents, std::layout_left>(md);
> + VERIFY(md.data_handle() == storage.data());
> + VERIFY(md.mapping() == m);
> + return true;
> +}
> +
> +constexpr bool
> +test_from_accessor()
> +{
> + constexpr size_t n = 3*5*7;
> + std::array<double, n> storage{};
> + using Extents = std::extents<int, 3, 5, 7>;
> +
> + auto exts = Extents{};
> + auto m = std::layout_left::mapping(exts);
> + auto a = std::default_accessor<double>{};
> + auto md = std::mdspan(storage.data(), m, a);
> +
> + assert_deduced_typedefs<double, Extents, std::layout_left>(md);
> + VERIFY(md.data_handle() == storage.data());
> + VERIFY(md.mapping() == m);
> + return true;
> +}
> +
> +void
> +test_from_int_like()
> +{
> + constexpr size_t n = 3*5*7;
> + std::array<double, n> storage{};
> +
> + auto verify = [&](auto md)
> + {
> + VERIFY(md.data_handle() == storage.data());
> + VERIFY(md.extent(0) == 3);
> + VERIFY(md.extent(1) == 5);
> + VERIFY(md.extent(2) == 7);
> +
> + VERIFY((md[IntLike(0), 0, IntLike(0)]) == 0.0);
> + auto zero = std::array{IntLike(0), IntLike(0), IntLike(0)};
> + auto zero_view = std::span<IntLike, 3>{zero};
> + VERIFY((md[zero]) == 0.0);
> + VERIFY((md[zero_view]) == 0.0);
> + };
> +
> + auto shape = std::array{IntLike(3), IntLike(5), IntLike(7)};
> + auto shape_view = std::span<IntLike, 3>{shape};
> + verify(std::mdspan(storage.data(), IntLike(3), 5, IntLike(7)));
> + verify(std::mdspan(storage.data(), shape));
> + verify(std::mdspan(storage.data(), shape_view));
> +}
> +
> +template<typename T>
> + class OpaqueAccessor
> + {
> + struct Handle
> + {
> + T * ptr;
> + };
> +
> + public:
> + using element_type = T;
> + using reference = T&;
> + using data_handle_type = Handle;
> + using offset_policy = OpaqueAccessor;
> +
> + reference
> + access(data_handle_type p, size_t i) const
> + {
> + ++access_count;
> + return p.ptr[i];
> + }
> +
> + typename offset_policy::data_handle_type
> + offset(data_handle_type p, size_t i) const
> + {
> + ++offset_count;
> + return typename offset_policy::data_handle_type{(void*)(p.ptr + i)};
> + }
> +
> + mutable size_t access_count = 0;
> + mutable size_t offset_count = 0;
> + };
> +
> +void
> +test_from_opaque_accessor()
> +{
> + constexpr size_t n = 3*5*7;
> + std::array<double, n> storage{};
> + using Extents = std::extents<int, 3, 5, 7>;
> +
> + auto exts = Extents{};
> + auto m = std::layout_left::mapping(exts);
> + auto a = OpaqueAccessor<double>{};
> + auto handle = OpaqueAccessor<double>::data_handle_type{storage.data()};
> + auto md = std::mdspan(handle, m, a);
> +
> + using MDSpan = decltype(md);
> + static_assert(std::same_as<MDSpan::accessor_type, decltype(a)>);
> +
> + VERIFY((md[0, 0, 0]) == 0.0);
> + VERIFY(md.accessor().access_count == 1);
> +
> + VERIFY((md[2, 4, 6]) == 0.0);
> + VERIFY(md.accessor().access_count == 2);
> +}
> +
> +template<typename T, typename Base>
> + class BaseClassAccessor
> + {
> + public:
> + using element_type = T;
> + using reference = Base&;
> + using data_handle_type = T*;
> + using offset_policy = BaseClassAccessor;
> +
> + static_assert(std::common_reference_with<reference&&, element_type&>);
> +
> + reference
> + access(data_handle_type p, size_t i) const
> + { return p[i]; }
> +
> + typename offset_policy::data_handle_type
> + offset(data_handle_type p, size_t i) const
> + { return typename offset_policy::data_handle_type{p + i}; }
> + };
> +
> +struct Base
> +{
> + double value = 1.0;
> +};
> +
> +struct Derived : Base
> +{
> + double value = 2.0;
> +};
> +
> +void
> +test_from_base_class_accessor()
> +{
> + constexpr size_t n = 3*5*7;
> + std::array<Derived, n> storage{};
> + using Extents = std::extents<int, 3, 5, 7>;
> +
> + auto exts = Extents{};
> + auto m = std::layout_left::mapping(exts);
> + auto a = BaseClassAccessor<Derived, Base>{};
> + auto md = std::mdspan(storage.data(), m, a);
> +
> + using MDSpan = decltype(md);
> + static_assert(std::same_as<MDSpan::accessor_type, decltype(a)>);
> + static_assert(std::same_as<decltype(md[0, 0, 0]), Base&>);
> + VERIFY((md[0, 0, 0].value) == 1.0);
> + VERIFY((md[2, 4, 6].value) == 1.0);
> +}
> +
> +constexpr bool
> +test_from_mapping_like()
> +{
> + double data = 1.1;
> + auto m = LayoutLike::mapping<std::extents<int, 1, 2, 3>>{};
> + auto md = std::mdspan(&data, m);
> + VERIFY((md[0, 0, 0]) == data);
> + VERIFY((md[0, 1, 2]) == data);
> + return true;
> +}
> +
> +template<typename MDSpan>
> + constexpr void
> + test_empty(MDSpan md)
> + {
> + VERIFY(md.empty() == (md.size() == 0));
> + }
> +
> +constexpr bool
> +test_empty_all()
> +{
> + test_empty(std::mdspan<double, std::extents<int, dyn>>{});
> + return true;
> +}
> +
> +constexpr bool
> +test_access()
> +{
> + using Extents = std::extents<int, 3, 5, 7>;
> + auto exts = Extents{};
> +
> + auto mapping = std::layout_left::mapping(exts);
> + constexpr size_t n = mapping.required_span_size();
> + std::array<double, n> storage{};
> +
> + auto md = std::mdspan(storage.data(), mapping);
> + static_assert(std::__mdspan::__mapping_alike<decltype(md)>);
> +
> + for(int i = 0; i < exts.extent(0); ++i)
> + for(int j = 0; j < exts.extent(1); ++j)
> + for(int k = 0; k < exts.extent(2); ++k)
> + {
> + std::array<int, 3> ijk{i, j, k};
> + storage[mapping(i, j, k)] = 1.0;
> + VERIFY((md[i, j, k]) == 1.0);
> + VERIFY((md[ijk]) == 1.0);
> + VERIFY((md[std::span(ijk)]) == 1.0);
> + storage[mapping(i, j, k)] = 0.0;
> + }
> + return true;
> +}
> +
> +constexpr bool
> +test_swap()
> +{
> + using Extents = std::dextents<int, 2>;
> + auto e1 = Extents{3, 5};
> + auto e2 = Extents{7, 11};
> +
> + std::array<double, 3*5> s1{};
> + std::array<double, 7*11> s2{};
> +
> + auto md1 = std::mdspan(s1.data(), e1);
> + auto md2 = std::mdspan(s2.data(), e2);
> +
> + std::swap(md1, md2);
> +
> + VERIFY(md1.data_handle() == s2.data());
> + VERIFY(md2.data_handle() == s1.data());
> +
> + VERIFY(md1.size() == s2.size());
> + VERIFY(md2.size() == s1.size());
> + return true;
> +}
> +
> +int
> +main()
> +{
> + test_typedefs_all();
> +
> + test_rank_all();
> + test_extent_all();
> + static_assert(test_extent_all());
> +
> + test_class_properties_all();
> + static_assert(test_class_properties_all());
> +
> + test_empty_all();
> + static_assert(test_empty_all());
> +
> + test_default_ctor();
> + static_assert(test_default_ctor());
> +
> + test_from_other();
> + static_assert(test_from_other());
> +
> + test_from_carray();
> + static_assert(test_from_carray());
> +
> + test_from_pointer_and_shape();
> + static_assert(test_from_pointer_and_shape());
> +
> + test_from_extents();
> + static_assert(test_from_extents());
> +
> + test_from_mapping();
> + static_assert(test_from_mapping());
> +
> + test_from_accessor();
> + static_assert(test_from_accessor());
> +
> + test_from_int_like();
> + test_from_opaque_accessor();
> + test_from_base_class_accessor();
> + test_from_mapping_like();
> + static_assert(test_from_mapping_like());
> +
> + test_access();
> + static_assert(test_access());
> +
> + test_swap();
> + static_assert(test_swap());
> + return 0;
> +}
> --
> 2.49.0
>
>
