23 Containers library [containers]

23.7 Views [views]

23.7.3 Multidimensional access [views.multidim]

23.7.3.3 Class template extents [mdspan.extents]

23.7.3.3.3 Constructors [mdspan.extents.cons]

template<class OtherIndexType, size_t... OtherExtents>
  constexpr explicit(see below)
    extents(const extents<OtherIndexType, OtherExtents...>& other) noexcept;

Constraints:

(1.1)
sizeof...(OtherExtents) == rank() is true.
(1.2)
((OtherExtents == dynamic_extent || Extents == dynamic_extent || OtherExtents ==
Extents) && ...) is true.

Preconditions:

(2.1)
other.extent(r) equals $E_{r}$ for each r for which $E_{r}$ is a static extent, and
(2.2)
either
- (2.2.1)
  sizeof...(OtherExtents) is zero, or
- (2.2.2)
  other.extent(r) is representable as a value of type index_type for every rank index r of other.

Postconditions: *this == other is true.

Remarks: The expression inside explicit is equivalent to: (((Extents != dynamic_extent) && (OtherExtents == dynamic_extent)) || ... ) || (numeric_limits<index_type>::max() < numeric_limits<OtherIndexType>::max())

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template<class... OtherIndexTypes>
  constexpr explicit extents(OtherIndexTypes... exts) noexcept;

Let N be sizeof...(OtherIndexTypes), and let exts_arr be array<index_type, N>{static_cast<
index_type>(std::move(exts))...}.

Constraints:

(6.1)
(is_convertible_v<OtherIndexTypes, index_type> && ...) is true,
(6.2)
(is_nothrow_constructible_v<index_type, OtherIndexTypes> && ...) is true, and
(6.3)
N == rank_dynamic() || N == rank() is true.
[Note 1:
One can construct extents from just dynamic extents, which are all the values getting stored, or from all the extents with a precondition.
— end note]

Preconditions:

(7.1)
If N != rank_dynamic() is true, exts_arr[r] equals $E_{r}$ for each r for which $E_{r}$ is a static extent, and
(7.2)
either
- (7.2.1)
  sizeof...(exts) == 0 is true, or
- (7.2.2)
  each element of exts is representable as a nonnegative value of type index_type.

Postconditions: *this == extents(exts_arr) is true.

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template<class OtherIndexType, size_t N>
  constexpr explicit(N != rank_dynamic())
    extents(span<OtherIndexType, N> exts) noexcept;
template<class OtherIndexType, size_t N>
  constexpr explicit(N != rank_dynamic())
    extents(const array<OtherIndexType, N>& exts) noexcept;

Constraints:

(9.1)
is_convertible_v<const OtherIndexType&, index_type> is true,
(9.2)
is_nothrow_constructible_v<index_type, const OtherIndexType&> is true, and
(9.3)
N == rank_dynamic() || N == rank() is true.

Preconditions:

(10.1)
If N != rank_dynamic() is true, exts[r] equals $E_{r}$ for each r for which $E_{r}$ is a static extent, and
(10.2)
either
- (10.2.1)
  N is zero, or
- (10.2.2)
  exts[r] is representable as a nonnegative value of type index_type for every rank index r.

Effects:

(11.1)
If N equals rank_dynamic(), for all d in the range [0, rank_dynamic()), direct-non-list-initializes dynamic-extents[d] with as_const(exts[d]).
(11.2)
Otherwise, for all d in the range [0, rank_dynamic()), direct-non-list-initializes dynamic-extents[d] with as_const(exts[dynamic-index-inv(d)]).

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template<class... Integrals>
  explicit extents(Integrals...) -> see below;

Constraints: (is_convertible_v<Integrals, size_t> && ...) is true.

Remarks: The deduced type is extents<size_t, maybe-static-ext<Integrals>...>.