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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_. 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))...). 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). 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
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
  • The program is ill-formed if:
  • 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]

See also

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