[mdspan.layout.stride.overview]

# 23 Containers library [[containers]](./#containers)

## 23.7 Views [[views]](views#mdspan.layout.stride.overview)

### 23.7.3 Multidimensional access [[views.multidim]](views.multidim#mdspan.layout.stride.overview)

#### 23.7.3.4 Layout mapping [[mdspan.layout]](mdspan.layout#stride.overview)

#### 23.7.3.4.7 Class template layout_stride​::​mapping [[mdspan.layout.stride]](mdspan.layout.stride#overview)

#### 23.7.3.4.7.1 Overview [mdspan.layout.stride.overview]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L22564)

layout_stride provides a layout mapping
where the strides are user-defined[.](#1.sentence-1)

namespace std {template<class Extents>class layout_stride::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 = layout_stride; private:static constexpr rank_type *rank_* = extents_type::rank(); // *exposition only*public:// [[mdspan.layout.stride.cons]](mdspan.layout.stride.cons "23.7.3.4.7.3 Constructors"), constructorsconstexpr mapping() noexcept; constexpr mapping(const mapping&) noexcept = default; template<class OtherIndexType>constexpr mapping(const extents_type&, span<OtherIndexType, *rank_*>) noexcept; template<class OtherIndexType>constexpr mapping(const extents_type&, const array<OtherIndexType, *rank_*>&) noexcept; template<class StridedLayoutMapping>constexpr explicit(*see below*) mapping(const StridedLayoutMapping&) noexcept; constexpr mapping& operator=(const mapping&) noexcept = default; // [[mdspan.layout.stride.obs]](mdspan.layout.stride.obs "23.7.3.4.7.4 Observers"), observersconstexpr const extents_type& extents() const noexcept { return *extents_*; }constexpr array<index_type, *rank_*> strides() const noexcept { return *strides_*; }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 false; }static constexpr bool is_always_strided() noexcept { return true; }static constexpr bool is_unique() noexcept { return true; }constexpr bool is_exhaustive() const noexcept; static constexpr bool is_strided() noexcept { return true; }constexpr index_type stride(rank_type i) const noexcept { return *strides_*[i]; }template<class OtherMapping>friend constexpr bool operator==(const mapping&, const OtherMapping&) noexcept; private: extents_type *extents_*{}; // *exposition only* array<index_type, *rank_*> *strides_*{}; // *exposition only*// [[mdspan.sub.map]](mdspan.sub.map "23.7.3.7.6 Specializations of submdspan_­mapping"), submdspan mapping specializationtemplate<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...); }};}

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L22636)

If Extents is not a specialization of extents,
then the program is ill-formed[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L22640)

layout_stride​::​mapping<E> is a trivially copyable type
that models [regular](concepts.object#concept:regular "18.6 Object concepts [concepts.object]") for each E[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L22644)

*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[.](#4.sentence-1)