std::Relation

 

C++

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Named requirements

Language support library

Concepts library (C++20)

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Strings library

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Technical Specifications

 

Concepts library

Core language concepts
Same DerivedFrom ConvertibleTo CommonReference Common	Integral SignedIntegral UnsignedIntegral Assignable SwappableSwappableWith	Destructible Constructible DefaultConstructible MoveConstructible CopyConstructible
Comparison concepts
Boolean	EqualityComparableEqualityComparableWith	StrictTotallyOrderedStrictTotallyOrderedWith
Object concepts
Movable Copyable	Semiregular Regular
Callable concepts
InvocableRegularInvocable	Predicate	Relation StrictWeakOrder

 

Defined in header <concepts>
template <class R, class T, class U> concept Relation =   std::Predicate<R, T, T> &&   std::Predicate<R, U, U> &&   std::CommonReference<     const std::remove_reference_t<T>&,     const std::remove_reference_t<U>&> &&   std::Predicate<R,     std::common_reference_t<       const std::remove_reference_t<T>&,       const std::remove_reference_t<U>&>,     std::common_reference_t<       const std::remove_reference_t<T>&,       const std::remove_reference_t<U>&>> &&   std::Predicate<R, T, U> &&   std::Predicate<R, U, T>;	(1)	(since C++20)

The concept Relation<R, T, U> specifies that R defines a binary relation over the set of expressions whose type and value category are those encoded by either T or U.

Given

• r, an expression such that decltype((r)) is R,
• t, an expression such that decltype((t)) is T,
• u, an expression such that decltype((u)) is U,

and let C be std::common_reference_t<const std::remove_reference_t<T>&, const std::remove_reference_t<U>&>,

then Relation<R, T, U> is satisfied only if

• bool(r(t, u)) == bool(r(C(t), C(u))) and
• bool(r(u, t)) == bool(r(C(u), C(t))).