[mdspan.layout.left.overview]

namespace std { template<class Extents> class layout_left::mapping { public: using extents_type = Extents; using index_type = extents_type::index_type; using size_type = extents_type::size_type; using rank_type = extents_type::rank_type; using layout_type = layout_left; / [mdspan.layout.left.cons], constructors constexpr mapping() noexcept = default; constexpr mapping(const mapping&) noexcept = default; constexpr mapping(const extents_type&) noexcept; template<class OtherExtents> constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const mapping<OtherExtents>&) noexcept; template<class OtherExtents> constexpr explicit(!is_convertible_v<OtherExtents, extents_type>) mapping(const layout_right::mapping<OtherExtents>&) noexcept; template<class LayoutLeftPaddedMapping> constexpr explicit(!is_convertible_v<typename LayoutLeftPaddedMapping::extents_type, extents_type>) mapping(const LayoutLeftPaddedMapping&) noexcept; template<class OtherExtents> constexpr explicit(see below) mapping(const layout_stride::mapping<OtherExtents>&); constexpr mapping& operator=(const mapping&) noexcept = default; / [mdspan.layout.left.obs], observers constexpr const extents_type& extents() const noexcept { return extents_; } constexpr index_type required_span_size() const noexcept; template<class. Indices> constexpr index_type operator()(Indices..) const noexcept; static constexpr bool is_always_unique() noexcept { return true; } static constexpr bool is_always_exhaustive() noexcept { return true; } static constexpr bool is_always_strided() noexcept { return true; } static constexpr bool is_unique() noexcept { return true; } static constexpr bool is_exhaustive() noexcept { return true; } static constexpr bool is_strided() noexcept { return true; } constexpr index_type stride(rank_type) const noexcept; template<class OtherExtents> friend constexpr bool operator=(const mapping&, const mapping<OtherExtents>&) noexcept; private: extents_type extents_{}; / exposition only / [mdspan.sub.map], submdspan mapping specialization template<class. SliceSpecifiers> constexpr auto submdspan-mapping-impl(SliceSpecifiers..) const / exposition only -> see below; template<class. SliceSpecifiers> friend constexpr auto submdspan_mapping( const mapping& src, SliceSpecifiers.. slices) { return src.submdspan-mapping-impl(slices..); } }; }

If Extents is not a specialization of extents, then the program is ill-formed.

layout_left::mapping<E> is a trivially copyable type that models regular for each E.

Mandates: If Extents::rank_dynamic() == 0 is true, then the size of the multidimensional index space Extents() is representable as a value of type typename Extents::index_type.