[mdspan.extents.cons]

# 23 Containers library [[containers]](./#containers)

## 23.7 Views [[views]](views#mdspan.extents.cons)

### 23.7.3 Multidimensional access [[views.multidim]](views.multidim#mdspan.extents.cons)

#### 23.7.3.3 Class template extents [[mdspan.extents]](mdspan.extents#cons)

#### 23.7.3.3.3 Constructors [mdspan.extents.cons]

[🔗](#lib:extents,constructor)

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

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21276)

*Constraints*: 

- [(1.1)](#1.1)

  sizeof...(OtherExtents) == rank() is true[.](#1.1.sentence-1)

- [(1.2)](#1.2)

  ((OtherExtents == dynamic_extent || Extents == dynamic_extent || OtherExtents ==  
Extents) && ...) is true[.](#1.2.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21285)

*Preconditions*: 

- [(2.1)](#2.1)

other.extent(r) equals Er for each r for which Er is a static extent, and

- [(2.2)](#2.2)

either
  * [(2.2.1)](#2.2.1)

sizeof...(OtherExtents) is zero, or

  * [(2.2.2)](#2.2.2)

other.extent(r) is representable as
a value of type index_type for every rank index r of other[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21302)

*Postconditions*: *this == other is true[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21306)

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

[🔗](#lib:extents,constructor_)

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

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21322)

Let N be sizeof...(OtherIndexTypes),
and let exts_arr bearray<index_type, N>{static_cast<  
index_type>(std​::​move(exts))...}[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21327)

*Constraints*: 

- [(6.1)](#6.1)

(is_convertible_v<OtherIndexTypes, index_type> && ...) is true,

- [(6.2)](#6.2)

(is_nothrow_constructible_v<index_type, OtherIndexTypes> && ...) is true, and

- [(6.3)](#6.3)

N == rank_dynamic() || N == rank() is true[.](#6.sentence-1)
  [*Note [1](#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[.](#6.3.sentence-2)
 — *end note*]

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21343)

*Preconditions*: 

- [(7.1)](#7.1)

If N != rank_dynamic() is true,exts_arr[r] equals Er for each r for which Er is a static extent, and

- [(7.2)](#7.2)

either
  * [(7.2.1)](#7.2.1)

sizeof...(exts) == 0 is true, or

  * [(7.2.2)](#7.2.2)

each element of exts is representable
as a nonnegative value of type index_type[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21361)

*Postconditions*: *this == extents(exts_arr) is true[.](#8.sentence-1)

[🔗](#lib:extents,constructor__)

`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;
`

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21377)

*Constraints*: 

- [(9.1)](#9.1)

is_convertible_v<const OtherIndexType&, index_type> is true,

- [(9.2)](#9.2)

is_nothrow_constructible_v<index_type, const OtherIndexType&> is true, and

- [(9.3)](#9.3)

N == rank_dynamic() || N == rank() is true[.](#9.sentence-1)

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21388)

*Preconditions*: 

- [(10.1)](#10.1)

If N != rank_dynamic() is true,exts[r] equals Er for each r for which Er is a static extent, and

- [(10.2)](#10.2)

either
  * [(10.2.1)](#10.2.1)

N is zero, or

  * [(10.2.2)](#10.2.2)

exts[r] is representable
as a nonnegative value of type index_type for every rank index r[.](#10.sentence-1)

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21405)

*Effects*: 

- [(11.1)](#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])[.](#11.1.sentence-1)

- [(11.2)](#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)])[.](#11.2.sentence-1)

[🔗](#lib:extents,constructor___)

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

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21427)

*Constraints*: (is_convertible_v<Integrals, size_t> && ...) is true[.](#12.sentence-1)

[13](#13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L21431)

*Remarks*: The deduced type is extents<size_t, [*maybe-static-ext*](span.syn#concept:maybe-static-ext "23.7.2.1 Header <span> synopsis [span.syn]")<Integrals>...>[.](#13.sentence-1)