NAME¶

std::common_with - std::common_with

Synopsis¶

Defined in header <concepts>
template< class T, class U >

concept common_with =
std::same_as<std::common_type_t<T, U>, std::common_type_t<U, T>>
&&
requires {
static_cast<std::common_type_t<T, U>>(std::declval<T>());
static_cast<std::common_type_t<T, U>>(std::declval<U>());
} && (since C++20)
std::common_reference_with<
std::add_lvalue_reference_t<const T>,
std::add_lvalue_reference_t<const U>> &&
std::common_reference_with<
std::add_lvalue_reference_t<std::common_type_t<T, U>>,
std::common_reference_t<
std::add_lvalue_reference_t<const T>,

std::add_lvalue_reference_t<const U>>>;

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

Semantic requirements

T and U model std::common_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_type_t<T, U>(t1) equals std::common_type_t<T, U>(t2) if and only if
t1 equals t2; and
* std::common_type_t<T, U>(u1) equals std::common_type_t<T, U>(u2) if and only if
u1 equals u2.

In other words, the conversion to the common 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_type determines the common type of a group of types
(C++11) (class template)
common_reference determines the common reference type of a group of types
basic_common_reference (class template)
(C++20)
common_reference_with specifies that two types share a common reference type
(C++20) (concept)