std::common_with

 

哋它亢++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

Language support library

Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (哋它亢++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (哋它亢++17)

Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

Concepts library

Core language concepts same_as derived_from convertible_to common_reference_with      common_with integral signed_integral unsigned_integral floating_point swappableswappable_with destructible constructible_from default_initializable move_constructible copy_constructible assignable_from

Comparison concepts equality_comparableequality_comparable_with totally_orderedtotally_ordered_with Object concepts movable copyable semiregular regular Callable concepts invocableregular_invocable predicate relation equivalence_relation strict_weak_order

Exposition-only concepts boolean-testable

 

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>());     } &&     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>>>;		(since 哋它亢++20)

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 (哋它亢++11)	determines the common type of a group of types (class template)
common_referencebasic_common_reference (哋它亢++20)	determines the common reference type of a group of types (class template)
common_reference_with (哋它亢++20)	specifies that two types share a common reference type (concept)