Dune::Std::mdspan< Element, Extents, LayoutPolicy, AccessorPolicy > Class Template Reference

A multi-dimensional non-owning array view. More...

#include <dune/common/std/mdspan.hh>

Public Member Functions
constexpr const mapping_type &	mapping () const noexcept
	Index mapping of a layout policy.
constexpr const accessor_type &	accessor () const noexcept
	The accessor policy object.
constexpr const data_handle_type &	data_handle () const noexcept
	The pointer to the underlying flat sequence.
constexpr bool	is_unique () const
	Return true only if for every i and j where (i != j || ...) => mapping(i...) != mapping(j...).
constexpr bool	is_exhaustive () const
	Return true only if for all k in the range [0, mapping.required_span_size() ) there exists an i such that mapping(i...) equals k.
constexpr bool	is_strided () const
	Return true only if for every rank index r of extents there exists an integer sr such that, for all i where (i+dr) is a multidimensional index in extents, mapping((i+dr)...) - mapping(i...) equals sr. *. More...
constexpr index_type	stride (rank_type r) const
	The stride along the specified dimension.

Static Public Member Functions
static constexpr bool	is_always_unique ()
	Return true only if for every i and j where (i != j || ...) => mapping(i...) != mapping(j...). More...
static constexpr bool	is_always_exhaustive ()
	Return true only if for all k in the range [0, mapping.required_span_size() ) there exists an i such that mapping(i...) equals k. More...
static constexpr bool	is_always_strided ()
	Return true only if for every rank index r of extents there exists an integer sr such that, for all i where (i+dr) is a multidimensional index in extents, mapping((i+dr)...) - mapping(i...) equals sr. *. More...

Related Functions
(Note that these are not member functions.)
constexpr const extents_type &	extents () const noexcept
	Number of elements in all dimensions of the tensor,.

mdspan constructors [mdspan.mdspan.cons]
template<class E = extents_type, class D = data_handle_type, class M = mapping_type, class A = accessor_type, std::enable_if_t<(E::rank_dynamic() > 0), int > = 0, std::enable_if_t< std::is_default_constructible_v< D >, int > = 0, std::enable_if_t< std::is_default_constructible_v< M >, int > = 0, std::enable_if_t< std::is_default_constructible_v< A >, int > = 0>
constexpr	mdspan ()
	Default constructor value-initializes all members.
template<class... IndexTypes, class E = extents_type, class M = mapping_type, class A = accessor_type, std::enable_if_t<(sizeof...(IndexTypes)==E::rank()||sizeof...(IndexTypes)==E::rank_dynamic()), int > = 0, std::enable_if_t<(... &&std::is_convertible_v< IndexTypes, index_type >), int > = 0, std::enable_if_t<(... &&std::is_nothrow_constructible_v< index_type, IndexTypes >), int > = 0, std::enable_if_t< std::is_constructible_v< M, E >, int > = 0, std::enable_if_t< std::is_default_constructible_v< A >, int > = 0>
constexpr	mdspan (data_handle_type p, IndexTypes... exts)
	Construct from the dynamic extents given as variadic list.
template<class IndexType , std::size_t N, std::enable_if_t< std::is_convertible_v< const IndexType &, index_type >, int > = 0, std::enable_if_t< std::is_nothrow_constructible_v< index_type, const IndexType & >, int > = 0, std::enable_if_t<(N==extents_type::rank_dynamic()||N==extents_type::rank()), int > = 0>
constexpr	mdspan (data_handle_type p, Std::span< IndexType, N > exts)
	Construct from the dynamic extents given as an array.
template<class IndexType , std::size_t N, std::enable_if_t< std::is_convertible_v< IndexType, index_type >, int > = 0, std::enable_if_t<(N==extents_type::rank_dynamic()||N==extents_type::rank()), int > = 0>
constexpr	mdspan (data_handle_type p, const std::array< IndexType, N > &exts)
	Construct from the dynamic extents given as an array.
template<class M = mapping_type, std::enable_if_t< std::is_constructible_v< M, const extents_type & >, int > = 0>
constexpr	mdspan (data_handle_type p, const extents_type &e)
	Construct from the pointer to the data of the tensor and its extents.
template<class A = accessor_type, std::enable_if_t< std::is_default_constructible_v< A >, int > = 0>
constexpr	mdspan (data_handle_type p, const mapping_type &m)
	Construct from the pointer to the data of the tensor and an index mapping.
constexpr	mdspan (data_handle_type p, const mapping_type &m, const accessor_type &a)
	Construct from the pointer to the data of the tensor, an index mapping, and an accessor.
template<class OtherElementType , class OtherExtends , class OtherLayoutPolicy , class OtherAccessor , std::enable_if_t< std::is_constructible_v< mapping_type, const typename OtherElementType::template mapping< OtherExtends > & >, int > = 0, std::enable_if_t< std::is_constructible_v< accessor_type, const OtherAccessor & >, int > = 0>
constexpr	mdspan (const mdspan< OtherElementType, OtherExtends, OtherLayoutPolicy, OtherAccessor > &other) noexcept
	Converting constructor.

Multi index access
template<class... Indices, std::enable_if_t<(sizeof...(Indices)==extents_type::rank()), int > = 0, std::enable_if_t<(... &&std::is_convertible_v< Indices, index_type >), int > = 0, std::enable_if_t<(... &&std::is_nothrow_constructible_v< index_type, Indices >), int > = 0>
constexpr reference	operator() (Indices... indices) const
	Access specified element at position i0,i1,... More...
template<class Index , class E = extents_type, std::enable_if_t< std::is_convertible_v< Index, index_type >, int > = 0, std::enable_if_t<(E::rank()==1), int > = 0>
constexpr reference	operator[] (Index index) const
	Access specified element at position [i0] For a rank one mdspan, the operator[i] is added to support bracket access before __cpp_multidimensional_subscript is supported.
template<class Index , std::enable_if_t< std::is_convertible_v< const Index &, index_type >, int > = 0, std::enable_if_t< std::is_nothrow_constructible_v< index_type, const Index & >, int > = 0>
constexpr reference	operator[] (Std::span< Index, extents_type::rank()> indices) const
	Access specified element at position [i0,i1,...].
template<class Index , std::enable_if_t< std::is_convertible_v< const Index &, index_type >, int > = 0, std::enable_if_t< std::is_nothrow_constructible_v< index_type, const Index & >, int > = 0>
constexpr reference	operator[] (const std::array< Index, extents_type::rank()> &indices) const
	Access specified element at position [i0,i1,...].

Size information
constexpr index_type	extent (rank_type r) const noexcept
	Number of elements in the r'th dimension of the tensor.
constexpr size_type	size () const noexcept
	The number of elements accessible by this multi-dimensional span.
constexpr bool	empty () const noexcept
	Checks if the size of the index space is zero.
static constexpr rank_type	rank () noexcept
	Number of dimensions of the tensor.
static constexpr rank_type	rank_dynamic () noexcept
	Number of dimensions of the tensor.
static constexpr std::size_t	static_extent (rank_type r) noexcept
	Number of elements in the r'th dimension of the tensor.

Detailed Description

template<class Element, class Extents, class LayoutPolicy = Std::layout_right, class AccessorPolicy = Std::default_accessor<Element>>
class Dune::Std::mdspan< Element, Extents, LayoutPolicy, AccessorPolicy >

A multi-dimensional non-owning array view.

The class mdspan is a view into a contiguous sequence of objects that reinterprets it as a multidimensional array.

The implementation is based in the standard proposal P0009r17 and the C++ standard working draft N4971.

Example:

std::vector v{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
 
// view data as contiguous memory representing 2 rows and 5 columns
// with row-major ordering.
auto ms = Dune::Std::mdspan(v.data(), 2, 5);
 
// write data using 2D view
for (std::size_t i = 0; i != ms.extent(0); i++)
    for (std::size_t j = 0; j != ms.extent(1); j++)
        ms(i, j) = i + j;   // or ms[i, j]

Note

The interface of Std::mdspan provides the operator[] with multiple indices overload only if available in c++23. For older c++ versions the operator() overload is implemented.

Template Parameters

Element	The element type; a complete object type that is neither an abstract class type nor an array type.
Extents	Specifies number of dimensions, their sizes, and which are known at compile time. Must be a specialization of Std::extents.
LayoutPolicy	Specifies how to convert multi-dimensional index to underlying flat index.
AccessorPolicy	Specifies how to convert underlying 1D index to a reference to Element.

Member Function Documentation

is_always_exhaustive()

template<class Element , class Extents , class LayoutPolicy = Std::layout_right, class AccessorPolicy = Std::default_accessor<Element>>

static constexpr bool Dune::Std::mdspan< Element, Extents, LayoutPolicy, AccessorPolicy >::is_always_exhaustive ( )

inlinestaticconstexpr

Return true only if for all k in the range [0, mapping.required_span_size() ) there exists an i such that mapping(i...) equals k.

is_always_strided()

template<class Element , class Extents , class LayoutPolicy = Std::layout_right, class AccessorPolicy = Std::default_accessor<Element>>

static constexpr bool Dune::Std::mdspan< Element, Extents, LayoutPolicy, AccessorPolicy >::is_always_strided ( )

inlinestaticconstexpr

Return true only if for every rank index r of extents there exists an integer sr such that, for all i where (i+dr) is a multidimensional index in extents, mapping((i+dr)...) - mapping(i...) equals sr. *.

Note

This implies that for a strided layout mapping(i0, ..., ik) = mapping(0, ..., 0) + i0 * s0 + ... + ik * sk.

is_always_unique()

template<class Element , class Extents , class LayoutPolicy = Std::layout_right, class AccessorPolicy = Std::default_accessor<Element>>

static constexpr bool Dune::Std::mdspan< Element, Extents, LayoutPolicy, AccessorPolicy >::is_always_unique ( )

inlinestaticconstexpr

Return true only if for every i and j where (i != j || ...) => mapping(i...) != mapping(j...).

is_strided()

template<class Element , class Extents , class LayoutPolicy = Std::layout_right, class AccessorPolicy = Std::default_accessor<Element>>

constexpr bool Dune::Std::mdspan< Element, Extents, LayoutPolicy, AccessorPolicy >::is_strided ( ) const

inlineconstexpr

Return true only if for every rank index r of extents there exists an integer sr such that, for all i where (i+dr) is a multidimensional index in extents, mapping((i+dr)...) - mapping(i...) equals sr. *.

Note

This implies that for a strided layout mapping(i0, ..., ik) = mapping(0, ..., 0) + i0 * s0 + ... + ik * sk.

operator()()

template<class Element , class Extents , class LayoutPolicy = Std::layout_right, class AccessorPolicy = Std::default_accessor<Element>>

template<class... Indices, std::enable_if_t<(sizeof...(Indices)==extents_type::rank()), int > = 0, std::enable_if_t<(... &&std::is_convertible_v< Indices, index_type >), int > = 0, std::enable_if_t<(... &&std::is_nothrow_constructible_v< index_type, Indices >), int > = 0>

constexpr reference Dune::Std::mdspan< Element, Extents, LayoutPolicy, AccessorPolicy >::operator() ( Indices...  indices ) const

inlineconstexpr

Access specified element at position i0,i1,...

Note

The operator() is not in the std proposal, but is provided for using mdspan without c++23.

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The documentation for this class was generated from the following file:

• dune/common/std/mdspan.hh