NAME¶

std::three_way_comparable,std::three_way_comparable_with - std::three_way_comparable,std::three_way_comparable_with

Synopsis¶

Defined in header <compare>
template< class T, class Cat = std::partial_ordering >

concept three_way_comparable =
__WeaklyEqualityComparableWith<T, T> &&
__PartiallyOrderedWith<T, T> && (1) (since C++20)
requires(const std::remove_reference_t<T>& a,
const std::remove_reference_t<T>& b) {
{ a <=> b } -> __ComparesAs<Cat>;

};
template< class T, class U, class Cat = std::partial_ordering >

concept three_way_comparable_with =
std::three_way_comparable<T, Cat> &&
std::three_way_comparable<U, Cat> &&
__ComparisonCommonTypeWith<T, U> &&
std::three_way_comparable<
std::common_reference_t<
const std::remove_reference_t<T>&, (2) (since C++20)
const std::remove_reference_t<U>&>, Cat> &&
__WeaklyEqualityComparableWith<T, U> &&
__PartiallyOrderedWith<T, U> &&
requires(const std::remove_reference_t<T>& t,
const std::remove_reference_t<U>& u) {
{ t <=> u } -> __ComparesAs<Cat>;
{ u <=> t } -> __ComparesAs<Cat>;

};
template< class T, class Cat >
(exposition
concept __ComparesAs = (3) only*)

std::same_as<std::common_comparison_category_t<T, Cat>, Cat>;

1) The concept std::three_way_comparable specifies that the three way comparison
operator <=> on T yield results consistent with the comparison category implied by
Cat.
2) The concept std::three_way_comparable_with specifies that the three way
comparison operator <=> on (possibly mixed) T and U operands yield results
consistent with the comparison category implied by Cat. Comparing mixed operands
yields results equivalent to comparing the operands converted to their common type.

__WeaklyEqualityComparableWith, __PartiallyOrderedWith, and
__ComparisonCommonTypeWith are exposition-only concepts. See descriptions of
equality_comparable and totally_ordered.

See also¶

equality_comparable specifies that operator == is an equivalence relation
equality_comparable_with (concept)
(C++20)
totally_ordered specifies that the comparison operators on the type yield a
totally_ordered_with total order
(C++20) (concept)