Defined in header <concepts> | ||
---|---|---|
template < class T, class U > concept CommonReference = std::Same<std::common_reference_t<T, U>, std::common_reference_t<U, T>> && std::ConvertibleTo<T, std::common_reference_t<T, U>> && std::ConvertibleTo<U, std::common_reference_t<T, U>>; | (since C++20) |
The concept CommonReference<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 CommonReference<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.
An expression is equality preserving if it results in equal outputs given equal inputs.
Every expression required to be equality preserving is further required to be stable: two evaluations of such an expression with the same input objects must have equal outputs absent any explicit intervening modification of those input objects.
(C++20) | determines the common reference type of a group of types (class template) |
(C++20) | specifies that two types share a common type (concept) |
(C++11) | determines the common type of a group of types (class template) |
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