std::mdspan<T,Extents,LayoutPolicy,AccessorPolicy>::operator[]

 

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std::mdspan

Member functions mdspan::mdspan mdspan::operator= Element access mdspan::operator[] Observers mdspan::rank mdspan::rank_dynamic mdspan::static_extent mdspan::extent mdspan::size mdspan::empty mdspan::stride mdspan::extents mdspan::data_handle mdspan::mapping mdspan::accessor mdspan::is_uniquemdspan::is_exhaustivemdspan::is_stridedmdspan::is_always_uniquemdspan::is_always_exhaustivemdspan::is_always_strided

Non-member functions swap(std::mdspan) Subviews submdspan (C++26) submdspan_extents (C++26) Helper types and templates extentsdextentsdims (C++26) default_accessor Layout mapping policies layout_left layout_right layout_stride layout_left_padded (C++26) layout_right_padded (C++26) Subviews helpers full_extent (C++26) strided_slice (C++26) submdspan_mapping_result (C++26) Deduction guides

 

template< class... OtherIndexTypes > constexpr reference operator[]( OtherIndexTypes... indices ) const;	(1)	(since C++23)
template< class OtherIndexType > constexpr reference operator[]     ( std::span<OtherIndexType, rank()> indices ) const;	(2)	(since C++23)
template< class OtherIndexType > constexpr reference operator[]     ( const std::array<OtherIndexType, rank()>& indices ) const;	(3)	(since C++23)

Returns a reference to the indices^th element of the mdspan.

1) Equivalent to return acc_.access(ptr_, map_(static_cast<index_type>(std::move(indices))...));.

This overload participates in overload resolution only if:

• (std::is_convertible_v<OtherIndexTypes, index_type> && ...) is true,
• (std::is_nothrow_constructible_v<index_type, OtherIndexTypes> && ...) is true, and
• sizeof...(OtherIndexTypes) == rank() is true.

Let I be extents_type::index-cast(std::move(indices)). Then the behavior is undefined if I is not a multidimensional index in extents(), i.e., map_(I) < map_.required_span_size() is false.

2,3) Let P be a parameter pack such that std::is_same_v<make_index_sequence<rank()>, index_sequence<P...>> is true, then the operator is equivalent to return operator[](extents_type::index-cast(std::as_const(indices[P]))...);.

This overload participates in overload resolution only if:

• std::is_convertible_v<const OtherIndexType&, index_type> is true, and
• std::is_nothrow_constructible_v<index_type, const OtherIndexType&> is true.

Parameters

indices

-

the indices of the element to access

Return value

A reference to the element.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3974	C++23	overloads (2,3) did not apply extents_type::index-cast	applies