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

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 all following values are true:

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

If extents_type::index-cast (std::move(indices)) is not a multidimensional index in extents(), the behavior is undefined.

(until C++26)

If extents_type::index-cast (std::move(indices)) is not a multidimensional index in extents():

If the implementation is hardened, a contract violation occurs.
If the implementation is not hardened, the behavior is undefined.

(since C++26)

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

This overload participates in overload resolution only if all following values are true:

std::is_convertible_v<const OtherIndexType&, index_type>
std::is_nothrow_constructible_v<index_type, const OtherIndexType&>

Parameters

indices

the indices of the element to access

Return value

A reference to the element.

Example

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

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

Parameters

Return value

Example

Defect reports

See also