std::mdspan<T,Extents,LayoutPolicy,AccessorPolicy>::mdspan

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

Views

span (C++20)

mdspan (C++23)

Iterator invalidation

Member function table

Non-member function table

 

std::mdspan

Member functions

mdspan::mdspan (C++23)

mdspan::operator= (C++23)

Element access

mdspan::operator[] (C++23)

Observers

mdspan::size (C++23)

mdspan::empty (C++23)

mdspan::stride (C++23)

mdspan::extents (C++23)

mdspan::data_handle (C++23)

mdspan::mapping (C++23)

mdspan::accessor (C++23)

mdspan::is_uniquemdspan::is_exhaustivemdspan::is_stridedmdspan::is_always_uniquemdspan::is_always_exhaustivemdspan::is_always_strided (C++23)(C++23)(C++23)(C++23)(C++23)(C++23)

Non-member functions

swap (C++23)

Helper types and templates

extentsdextents (C++23)(C++23)

layout_right (C++23)

layout_left (C++23)

layout_stride (C++23)

default_accessor (C++23)

Deduction guides(C++23)

 

constexpr mdspan();	(1)	(since C++23)
template< class... OtherIndexTypes >   constexpr explicit mdspan( data_handle_type p, OtherIndexTypes... exts );	(2)	(since C++23)
template< class OtherIndexType, std::size_t N >   constexpr explicit(N != rank_dynamic())     mdspan( data_handle_type p, std::span<OtherIndexType, N> exts );	(3)	(since C++23)
template< class OtherIndexType, std::size_t N >   constexpr explicit(N != rank_dynamic())     mdspan( data_handle_type p, const std::array<OtherIndexType, N>& exts );	(4)	(since C++23)
constexpr mdspan( data_handle_type p, const extents_type& ext );	(5)	(since C++23)
constexpr mdspan( data_handle_type p, const mapping_type& m );	(6)	(since C++23)
constexpr mdspan( data_handle_type p, const mapping_type& m,                   const accessor_type& a );	(7)	(since C++23)
template< class OtherElementType, class OtherExtents,           class OtherLayoutPolicy, class OtherAccessor >   constexpr explicit(/* see below */)     mdspan( const mdspan<OtherElementType, OtherExtents,                          OtherLayoutPolicy, OtherAccessor>& other );	(8)	(since C++23)
constexpr mdspan( const mdspan& rhs ) = default;	(9)	(since C++23)
constexpr mdspan( mdspan&& rhs ) = default;	(10)	(since C++23)

Construct an mdspan.

1) Construct an empty mdspan. Value-initializes ptr_, map_, and acc_.

• The behavior is undefined if [​0​, map_.required_span_size()) is not an accessible range of ptr_ and acc_ for the values of map_ and acc_ after the invocation of this constructor.
• This overload participates in overload resolution only if

• rank_dynamic() > 0 is true,
• std::is_default_constructible_v<data_handle_type> is true,
• std::is_default_constructible_v<mapping_type> is true, and
• std::is_default_constructible_v<accessor_type> is true.

2) Construct an mdspan over the underlying data referred by p with extents represented by exts.... Value-initializes acc_, direct-non-list-initializes ptr_ with std::move(p) and map_ with extents_type(static_cast<index_type>(std::move(exts))...).

• The behavior is undefined if [​0​, map_.required_span_size()) is not an accessible range of ptr_ and acc_ for the values of map_ and acc_ after the invocation of this constructor.
• Let N be sizeof...(OtherIndexTypes). This overload participates in overload resolution only if

• (std::is_convertible_v<OtherIndexTypes, index_type> && ...) is true,
• (std::is_nothrow_constructible<index_type, OtherIndexTypes> && ...) is true,
• N == rank() || N == rank_dynamic() is true,
• std::is_constructible_v<mapping_type, extents_type> is true, and
• std::is_default_constructible_v<accessor_type> is true.

3,4) Construct an mdspan over the underlying data referred by p with extents represented by pack exts. Value-initializes acc_, direct-non-list-initializes ptr_ with std::move(p) and map_ with extents_type(exts).

• The behavior is undefined if [​0​, map_.required_span_size()) is not an accessible range of ptr_ and acc_ for the values of map_ and acc_ after the invocation of this constructor.
• This overload participates in overload resolution only if

• std::is_convertible_v<const OtherIndexTypes&, index_type> is true,
• std::is_nothrow_constructible<index_type, const OtherIndexTypes&> is true,
• N == rank() || N == rank_dynamic() is true,
• std::is_constructible_v<mapping_type, extents_type> is true, and
• std::is_default_constructible_v<accessor_type> is true.

5) Construct an mdspan over the underlying data referred by p with extents represented by ext. Value-initializes acc_, direct-non-list-initializes ptr_ with std::move(p) and map_ with exts.

• The behavior is undefined if [​0​, map_.required_span_size()) is not an accessible range of p and acc_ for the values of map_ and acc_ after the invocation of this constructor.
• This overload participates in overload resolution only if

• std::is_constructible_v<mapping_type, const mapping_type&> is true, and
• std::is_default_constructible_v<accessor_type> is true.

6) Construct an mdspan over the underlying data referred by p with layout mapping m. Value-initializes acc_, direct-non-list-initializes ptr_ with std::move(p) and map_ with m.

• The behavior is undefined if [​0​, m.required_span_size()) is not an accessible range of p and acc_ for the values of acc_ after the invocation of this constructor.
• This overload participates in overload resolution only if std::is_default_constructible_v<accessor_type> is true.

7) Construct an mdspan over the underlying data referred by p with layout mapping m and accessor a. Direct-non-list-initializes ptr_ with std::move(p), map_ with m and acc_ with a.

• The behavior is undefined if [​0​, m.required_span_size()) is not an accessible range of p and a after the invocation of this constructor.

8) Converting constructor from another mdspan. Direct-non-list-initializes ptr_ with other.ptr_, map_ with other.map_ and acc_ with other.acc_.

• The behavior is undefined if :

• [​0​, map_.required_span_size()) is not an accessible range of ptr_ and acc_ for the values of map_ and acc_ after the invocation of this constructor, or
• for each rank index r of extents_type,    extents_type::static_extent(r) == std::dynamic_extent
  || extents_type::static_extent(r) == other.extent(r) is false.

• This overload participates in overload resolution only if

• std::is_constructible_v<mapping_type, const OtherLayoutPolicy​::
      ​template mapping<OtherExtents>&> is true, and
• std::is_constructible_v<accessor_type, const OtherAccessor&> is true.

• The program is ill-formed if:

• std::is_constructible_v<data_handle_type,
      const OtherAccessor​::​data_handle_type&> is false, or
• std::is_constructible_v<extents_type, OtherExtents> is false.

• The expression inside explicit is equivalent to:    !std::is_convertible_v<const OtherLayoutPolicy::
         template mapping<OtherExtents>&, mapping_type>
  || !std::is_convertible_v<const OtherAccessor&, accessor_type>

9) Defaulted copy constructor.

10) Defaulted move constructor.

Parameters

p	-	a handle to the underlying data
m	-	a layout mapping
a	-	an accessor
ext	-	represents a one-dimensional extents
exts	-	represents a multi-dimensional extents
other	-	another mdspan to convert from
rhs	-	another mdspan to copy or move from

References

• C++23 standard (ISO/IEC 14882:2023):

• 24.7.3.6.2 Constructors [mdspan.mdspan.cons]