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

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, optionally using user-supplied data handle p, layout mapping m, and accessor a. If extents exts or ext are supplied, they are converted to extents_type and used to initialize the layout mapping.

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	-	a `std::extents` object
exts	-	represents a multi-dimensional extents
other	-	another mdspan to convert from
rhs	-	another mdspan to copy or move from

Example

References

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

24.7.3.6.2 Constructors [mdspan.mdspan.cons]

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

Parameters

Example

References

See also