23 Containers library [containers]

23.7 Views [views]

23.7.3 Multidimensional access [views.multidim]

23.7.3.7 submdspan [mdspan.sub]

23.7.3.7.4 Exposition-only helpers [mdspan.sub.helpers]

template<class T>
  constexpr T de-ice(T val) { return val; }
template<integral-constant-like T>
  constexpr auto de-ice(T) { return T::value; }

template<class IndexType, size_t k, class... SliceSpecifiers>
  constexpr IndexType first_(SliceSpecifiers... slices);

Mandates: IndexType is a signed or unsigned integer type.

Let

ϕ_{k}

denote the following value:

(2.1)
$s_{k}$ if $S_{k}$ models convertible_to<IndexType>;
(2.2)
otherwise, get<0>( $s_{k}$ ) if $S_{k}$ models index-pair-like<IndexType>;
(2.3)
otherwise, de-ice( $s_{k}$ .offset) if $S_{k}$ is a specialization of strided_slice;
(2.4)
otherwise, 0.

Preconditions:

ϕ_{k}

is representable as a value of type IndexType.

Returns: extents<IndexType>::index-cast(

ϕ_{k}

🔗

template<size_t k, class Extents, class... SliceSpecifiers>
  constexpr auto last_(const Extents& src, SliceSpecifiers... slices);

Mandates: Extents is a specialization of extents.

Let index_type be typename Extents::index_type.

Let

λ_{k}

denote the following value:

(7.1)
de-ice( $s_{k}$ ) + 1 if $S_{k}$ models convertible_to<index_type>; otherwise
(7.2)
get<1>( $s_{k}$ ) if $S_{k}$ models index-pair-like<index_type>; otherwise
(7.3)
de-ice( $s_{k}$ .offset) + de-ice( $s_{k}$ .extent) if $S_{k}$ is a specialization of strided_slice; otherwise
(7.4)
src.extent(k).

Preconditions:

λ_{k}

is representable as a value of type index_type.

Returns: Extents::index-cast(

λ_{k}

🔗

template<class IndexType, size_t N, class... SliceSpecifiers>
  constexpr array<IndexType, sizeof...(SliceSpecifiers)>
    src-indices(const array<IndexType, N>& indices, SliceSpecifiers... slices);

Mandates: IndexType is a signed or unsigned integer type.

Returns: An array<IndexType, sizeof...(SliceSpecifiers)> src_idx such that for each k in the range [0, sizeof...(SliceSpecifiers)), src_idx[k] equals

(11.1)
first_<IndexType, k>(slices...) for each k where map-rank[k] equals dynamic_extent,
(11.2)
otherwise, first_<IndexType, k>(slices...) + indices[map-rank[k]].