std::common_reference_with

 

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Concepts library

Core language concepts same_as (C++20) derived_from (C++20) convertible_to (C++20) common_reference_with (C++20) common_with (C++20) integral (C++20) signed_integral (C++20) unsigned_integral (C++20) floating_point (C++20) swappableswappable_with (C++20)(C++20) destructible (C++20) constructible_from (C++20) default_initializable (C++20)   move_constructible (C++20) copy_constructible (C++20) assignable_from (C++20)

Comparison concepts equality_comparableequality_comparable_with (C++20)(C++20) totally_orderedtotally_ordered_with (C++20)(C++20) Object concepts movable (C++20) copyable (C++20) semiregular (C++20) regular (C++20) Callable concepts invocableregular_invocable (C++20)(C++20) predicate (C++20) relation (C++20) equivalence_relation (C++20) strict_weak_order (C++20)

Exposition-only concepts boolean-testable  (C++20)

 

Defined in header <concepts>
template < class T, class U > concept common_reference_with =   std::same_as<std::common_reference_t<T, U>, std::common_reference_t<U, T>> &&   std::convertible_to<T, std::common_reference_t<T, U>> &&   std::convertible_to<U, std::common_reference_t<T, U>>;		(since C++20)

The concept common_reference_with<T, U> specifies that two types T and U share a common reference type (as computed by std::common_reference_t) to which both can be converted.

T and U model common_reference_with<T, U> only if, given equality-preserving expressions t1, t2, u1 and u2 such that decltype((t1)) and decltype((t2)) are both T and decltype((u1)) and decltype((u2)) are both U,

• std::common_reference_t<T, U>(t1) equals std::common_reference_t<T, U>(t2) if and only if t1 equals t2; and
• std::common_reference_t<T, U>(u1) equals std::common_reference_t<T, U>(u2) if and only if u1 equals u2.

In other words, the conversion to the common reference type must preserve equality.

Equality preservation

Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).

See also

common_referencebasic_common_reference (C++20)	determines the common reference type of a group of types (class template)
common_with (C++20)	specifies that two types share a common type (concept)
common_type (C++11)	determines the common type of a group of types (class template)