24 Containers library [containers]

24.7 Views [views]

24.7.3 Multidimensional access [views.multidim]

24.7.3.4 Layout mapping [mdspan.layout]

24.7.3.4.7 Class template layout_stride::mapping [mdspan.layout.stride]

24.7.3.4.7.2 Exposition-only helpers [mdspan.layout.stride.expo]

Let REQUIRED-SPAN-SIZE(e, strides) be:

(1.1)
1, if e.rank() == 0 is true,
(1.2)
otherwise 0, if the size of the multidimensional index space e is 0,
(1.3)
otherwise 1 plus the sum of products of (e.extent(r) - 1) and extents_type::index-cast(strides[r]) for all r in the range [0, e.rank()).

Let OFFSET(m) be:

(2.1)
m(), if e.rank() == 0 is true,
(2.2)
otherwise 0, if the size of the multidimensional index space e is 0,
(2.3)
otherwise m(z...) for a pack of integers z that is a multidimensional index in m.extents() and each element of z equals 0.

Let is-extents be the exposition-only variable template defined as follows: template<class T> constexpr bool is-extents = false; // exposition only template<class IndexType, size_t... Args> constexpr bool is-extents<extents<IndexType, Args...>> = true; // exposition only

Let layout-mapping-alike be the exposition-only concept defined as follows: template<class M> concept layout-mapping-alike = requires { // exposition only requires is-extents<typename M::extents_type>; { M::is_always_strided() } -> same_as<bool>; { M::is_always_exhaustive() } -> same_as<bool>; { M::is_always_unique() } -> same_as<bool>; bool_constant<M::is_always_strided()>::value; bool_constant<M::is_always_exhaustive()>::value; bool_constant<M::is_always_unique()>::value; };

[Note 1:

This concept checks that the functions M::is_always_strided(), M::is_always_exhaustive(), and M::is_always_unique() exist, are constant expressions, and have a return type of bool.