23 Containers library [containers]

23.7 Views [views]

23.7.3 Multidimensional access [views.multidim]

23.7.3.3 Class template extents [mdspan.extents]

23.7.3.3.1 Overview [mdspan.extents.overview]

The class template extents represents a multidimensional index space of rank equal to sizeof.(Extents).

In [views], extents is used synonymously with multidimensional index space.

namespace std { template<class IndexType, size_t.. Extents> class extents { public: using index_type = IndexType; using size_type = make_unsigned_t<index_type>; using rank_type = size_t; / [mdspan.extents.obs], observers of the multidimensional index space static constexpr rank_type rank() noexcept { return sizeof.(Extents); } static constexpr rank_type rank_dynamic() noexcept { return dynamic-index(rank(); } static constexpr size_t static_extent(rank_type) noexcept; constexpr index_type extent(rank_type) const noexcept; / [mdspan.extents.cons], constructors constexpr extents() noexcept = default; template<class OtherIndexType, size_t.. OtherExtents> constexpr explicit(see below) extents(const extents<OtherIndexType, OtherExtents..>&) noexcept; template<class. OtherIndexTypes> constexpr explicit extents(OtherIndexTypes..) noexcept; template<class OtherIndexType, size_t N> constexpr explicit(N != rank_dynamic() extents(span<OtherIndexType, N>) noexcept; template<class OtherIndexType, size_t N> constexpr explicit(N != rank_dynamic() extents(const array<OtherIndexType, N>&) noexcept; / [mdspan.extents.cmp], comparison operators template<class OtherIndexType, size_t.. OtherExtents> friend constexpr bool operator=(const extents&, const extents<OtherIndexType, OtherExtents..>&) noexcept; / [mdspan.extents.expo], exposition-only helpers constexpr size_t fwd-prod-of-extents(rank_type) const noexcept; / exposition only constexpr size_t rev-prod-of-extents(rank_type) const noexcept; / exposition only template<class OtherIndexType> static constexpr auto index-cast(OtherIndexType&&) noexcept; / exposition only private: static constexpr rank_type dynamic-index(rank_type) noexcept; / exposition only static constexpr rank_type dynamic-index-inv(rank_type) noexcept; / exposition only array<index_type, rank_dynamic()> dynamic-extents{}; / exposition only }; template<class. Integrals> explicit extents(Integrals..) -> see below; }

Mandates:

(1.1)
IndexType is a signed or unsigned integer type, and
(1.2)
each element of Extents is either equal to dynamic_extent, or is representable as a value of type IndexType.

Each specialization of extents models regular and is trivially copyable.

Let

{E r be the {r th element of Extents .}^{th element of Extents .}}_{r be the {r th element of Extents .}^{th element of Extents .}}

{E r is a dynamic extent if it is equal to dynamic_extent, otherwise {E r is a static extent .}_{r is a static extent .}}_{r is a dynamic extent if it is equal to dynamic_extent, otherwise {E r is a static extent .}_{r is a static extent .}}

Let

{D r be the value of dynamic-extents [dynamic-index (r)] if {E r is a dynamic extent, otherwise {E r .}_{r .}}_{r is a dynamic extent, otherwise {E r .}_{r .}}}_{r be the value of dynamic-extents [dynamic-index (r)] if {E r is a dynamic extent, otherwise {E r .}_{r .}}_{r is a dynamic extent, otherwise {E r .}_{r .}}}

The

{r th interval of the multidimensional index space represented by an extents object is [0, {D r) .}_{r) .}}^{th interval of the multidimensional index space represented by an extents object is [0, {D r) .}_{r) .}}