C++ named requirements:AccessorPolicy(since C++23)

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AccessorPolicy defines how elements are accessed from a given data handle to such elements and an index. It is used as a policy instd::mdspan to specify the access to a reference of an element using an underlying 1D index.

[edit]Requirements

A typeA satisfiesAccessorPolicy if it modelscopyable, and the following aretrue:

And, given the following types and values, the expressions shown in the table below are valid and have the indicated semantics:

[edit]Legend

Type	Definition
`A`	an accessor policy type
`OP`	an offset policy type
Value	Definition
a	a value of type (possibly const-qualified)`A`
p	a value of type (possibly const-qualified)`A::data_handle_type`
i,j,n	values of typestd::size_t

[edit]Member types

Type	Definition	Requirements
`A::element_type`	unspecified	A complete object type that is not an abstract class type
`A::data_handle_type`	unspecified^[1]	Models`copyable` The following values are alltrue: std::is_nothrow_move_constructible_v <typename A::data_handle_type> std::is_nothrow_move_assignable_v <typename A::data_handle_type> std::is_nothrow_swappable_v <typename A::data_handle_type>
`A::reference`	unspecified^[2]	std::common_reference_with<typename A::reference&&, typename A::element_type&> istrue
`A::offset_policy`	`OP`	Satisfies the requirements ofAccessorPolicy std::constructible_from<OP,const A&> istrue typename OP::element_type andtypename A::element_type are the same type

↑Not required to beelement_type*.
↑Not required to beelement_type&.

[edit]Member functions

Expression Return type Semantics

Expression	Return type	Semantics
a.access(p, i)	typename A::reference	The expression isequality-preserving.
a.offset(p, i)	typename A::offset_policy ::data_handle_type	A valueq such that forb beingA::offset_policy(a), and any integern for which`[`0`,` n`)` is an accessible range (see below) ofp anda. `[`0`,` n- i`)` is an accessible range ofq andb; and b.access(q, j) provides access to the same element asa.access(p, i+ j), for everyj in the range`[`0`,` n- i`)`. The expression isequality-preserving.

a.access(p, i)

typename A::reference

The expression isequality-preserving.

a.offset(p, i)

typename A::offset_policy
::data_handle_type

A valueq such that forb beingA::offset_policy(a), and any integern for which[0, n) is an accessible range (see below) ofp anda.

[0, n- i) is an accessible range ofq andb; and
b.access(q, j) provides access to the same element asa.access(p, i+ j), for everyj in the range[0, n- i).

The expression isequality-preserving.

[edit]Accessible range

A range of indices[0, N) is anaccessible range of a given data handle and an accessor if, for each index in the range, theaccess member function produces a valid reference to an element.

[edit]Standard library

The following standard library types satisfyAccessorPolicy requirements:

default_accessor (C++23)	a type for indexed access to elements of`mdspan` (class template)[edit]
aligned_accessor (C++26)	a type for aligned access to elements of`mdspan` (class template)[edit]
Defined in namespace`std::linalg`
scaled_accessor (C++26)	std::mdspan accessor policy whose reference represents the product of a scaling factor that is fixed and its nestedstd::mdspan accessor's reference (class template)[edit]
conjugated_accessor (C++26)	std::mdspan accessor policy whose reference represents the complex conjugate of its nestedstd::mdspan accessor's reference (class template)[edit]