23 Containers library [containers]

23.7 Views [views]

23.7.3 Multidimensional access [views.multidim]

23.7.3.7 submdspan [mdspan.sub]

23.7.3.7.6 subextents function [mdspan.sub.extents]

template<class IndexType, size_t... Extents, class... SliceSpecifiers>
  constexpr auto subextents(const extents<IndexType, Extents...>& src,
                            SliceSpecifiers... raw_slices);

Let slices be the pack introduced by the following declaration: auto [...slices] = canonical_slices(src, raw_slices...);

Constraints: sizeof...(SliceSpecifiers) equals sizeof...(Extents).

Mandates: For each rank index k of src:

(3.1)
SliceSpecifiers...[k] is a submdspan slice type for IndexType, and
(3.2)
decltype(slices...[k]) is a valid submdspan slice type for the $k^{th}$ extent of extents<IndexType, Extents...>.

Preconditions: For each rank index k of src, slices...[k] is a valid submdspan slice for the

k^{th}

extent of src.

Let SubExtents be a specialization of extents such that:

(5.1)
SubExtents::rank() equals MAP_RANK(slices, Extents::rank()); and
(5.2)
for each rank index k of extents<IndexType, Extents...> such that the type of slices...[k] is not a collapsing slice type, SubExtents::static_extent(MAP_RANK(slices, k)) equals the following, where $Σ_{k}$ denotes the type of slices...[k]:
- (5.2.1)
  Extents::static_extent(k) if $Σ_{k}$ denotes full_extent_t; otherwise
- (5.2.2)
  $Σ_{k}$ ::extent_type::value if $Σ_{k}$ is a specialization of extent_slice whose extent_type denotes a specialization of constant_wrapper;
- (5.2.3)
  otherwise, dynamic_extent.

Returns: A value ext of type SubExtents such that for each rank index k of extents<IndexType, Extents...>, where the type of slices...[k] is not a collapsing slice type, ext.extent(MAP_RANK(slices, k)) equals the following, where

σ_{k}

denotes slices...[k]:

(6.1)
$σ_{k}$ .extent if the type of $σ_{k}$ is a specialization of extent_slice,
(6.2)
otherwise, $U - L$ , where [L, U) is the submdspan slice range of $σ_{k}$ for the $k^{th}$ extent of src.