std::mdspan::mdspan(3)

🎀 NAME 🎀

okay bestie, this is the page for std::mdspan::mdspan from the C++ Standard Libary manual — yes, that's how it's spelled here, and yes, the page title is exactly std::mdspan::mdspan(3) 💅

The name line is literally:

std::mdspan::mdspan - std::mdspan::mdspan

self-referential icon behavior, we love to see it ✨

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✨ Synopsis ✨

These are all ten constructor overloads, and every single one is since C++23 because we're fancy like that 🫶

(1) — since C++23

constexpr mdspan();

(2) — since C++23

template< class... OtherIndexTypes >
constexpr explicit mdspan( data_handle_type p, OtherIndexTypes... exts );

(3) — 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 );

(4) — 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 );

(5) — since C++23

constexpr mdspan( data_handle_type p, const extents_type& ext );

(6) — since C++23

constexpr mdspan( data_handle_type p, const mapping_type& m );

(7) — since C++23

constexpr mdspan( data_handle_type p, const mapping_type& m,
                  const accessor_type& a );

(8) — since C++23

template< class OtherElementType, class OtherExtents,
          class OtherLayoutPolicy, class OtherAccessor >
constexpr explicit(/* see below */)
    mdspan( const mdspan<OtherElementType, OtherExtents,
                         OtherLayoutPolicy, OtherAccessor>& other );

(9) — since C++23

constexpr mdspan( const mdspan& rhs ) = default;

(10) — since C++23

constexpr mdspan( mdspan&& rhs ) = default;

okay so here's the actual construction tea ☕

Constructs 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. periodt.

(1)

Constructs 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)

Constructs 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)

Constructs 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)

Constructs 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)

Constructs 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)

Constructs 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.

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🌸 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

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🧚 Example 🧚

This section is incomplete

Reason: no example

(no cap, that's literally what it says 😭)

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🔥 References 🔥

• C++23 standard (ISO/IEC 14882:2023):
• 24.7.3.6.2 Constructors [mdspan.mdspan.cons]

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🦋 See also 🦋

This section is incomplete

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👑 Categories 👑

• Todo no example
• Todo without reason

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okay that's the whole constructor saga 💖 source: cppreference.com; version/date: 2024.06.10; page: std::mdspan::mdspan(3) — slay and goodbye bestie 🫶✨