Standard library header  (C++20) (original) (raw)

This header is part of the language support library.

[edit] Synopsis

namespace std { // comparison category types class partial_ordering; class weak_ordering; class strong_ordering;   // named comparison functions constexpr bool is_eq (partial_ordering cmp) noexcept { return cmp == 0; } constexpr bool is_neq (partial_ordering cmp) noexcept { return cmp != 0; } constexpr bool is_lt (partial_ordering cmp) noexcept { return cmp < 0; } constexpr bool is_lteq(partial_ordering cmp) noexcept { return cmp <= 0; } constexpr bool is_gt (partial_ordering cmp) noexcept { return cmp > 0; } constexpr bool is_gteq(partial_ordering cmp) noexcept { return cmp >= 0; }   // common comparison category type template<class... Ts> struct common_comparison_category { using type = /* see description /; }; template<class... Ts> using common_comparison_category_t = typename common_comparison_category<Ts...>::type;   // concept three_way_comparable template<class T, class Cat = partial_ordering> concept three_way_comparable = / see description /; template<class T, class U, class Cat = partial_ordering> concept three_way_comparable_with = / see description /;   // result of three-way comparison template<class T, class U = T> struct compare_three_way_result;   template<class T, class U = T> using compare_three_way_result_t = typename compare_three_way_result<T, U>::type;   // class compare_three_way struct compare_three_way;   // comparison algorithms inline namespace / unspecified / { inline constexpr / unspecified / strong_order = / unspecified /; inline constexpr / unspecified / weak_order = / unspecified /; inline constexpr / unspecified / partial_order = / unspecified /; inline constexpr / unspecified / compare_strong_order_fallback = / unspecified /; inline constexpr / unspecified / compare_weak_order_fallback = / unspecified /; inline constexpr / unspecified / compare_partial_order_fallback = / unspecified */; } }

[edit] Concept three_way_comparable

namespace std { template<class T, class Cat> concept __ComparesAs = // exposition only same_as<common_comparison_category_t<T, Cat>, Cat>;   template<class T, class U> concept __PartiallyOrderedWith = // exposition only requires(const remove_reference_t& t, const remove_reference_t& u) { { t < u } -> boolean-testable; { t > u } -> boolean-testable; { t <= u } -> boolean-testable; { t >= u } -> boolean-testable; { u < t } -> boolean-testable; { u > t } -> boolean-testable; { u <= t } -> boolean-testable; { u >= t } -> boolean-testable; };   template<class T, class Cat = partial_ordering> concept three_way_comparable = __WeaklyEqualityComparableWith<T, T> && __PartiallyOrderedWith<T, T> && requires(const remove_reference_t& a, const remove_reference_t& b) { { a <=> b } -> __ComparesAs; }; }

[edit] Concept three_way_comparable_with

namespace std { template<class T, class U, class Cat = partial_ordering> concept three_way_comparable_with = __WeaklyEqualityComparableWith<T, U> && __PartiallyOrderedWith<T, U> && three_way_comparable<T, Cat> && three_way_comparable<U, Cat> && common_reference_with<const remove_reference_t&, const remove_reference_t&> && three_way_comparable< common_reference_t< const remove_reference_t&, const remove_reference_t&>, Cat> && requires(const remove_reference_t& t, const remove_reference_t& u) { { t <=> u } -> __ComparesAs; { u <=> t } -> __ComparesAs; }; }

[edit] Class std::partial_ordering

namespace std { class partial_ordering { int value; // exposition only bool is_ordered; // exposition only   // exposition-only constructors constexpr explicit partial_ordering(eq v) noexcept : value(int(v)), is_ordered(true) {} // exposition only constexpr explicit partial_ordering(ord v) noexcept : value(int(v)), is_ordered(true) {} // exposition only constexpr explicit partial_ordering(ncmp v) noexcept : value(int(v)), is_ordered(false) {} // exposition only   public: // valid values static const partial_ordering less; static const partial_ordering equivalent; static const partial_ordering greater; static const partial_ordering unordered;   // comparisons friend constexpr bool operator==(partial_ordering v, /* unspecified /) noexcept; friend constexpr bool operator==(partial_ordering v, partial_ordering w) noexcept = default; friend constexpr bool operator< (partial_ordering v, /* unspecified */) noexcept; friend constexpr bool operator> (partial_ordering v, / unspecified /) noexcept; friend constexpr bool operator<=(partial_ordering v, /* unspecified */) noexcept; friend constexpr bool operator>=(partial_ordering v, / unspecified /) noexcept; friend constexpr bool operator< (/* unspecified */, partial_ordering v) noexcept; friend constexpr bool operator> (/ unspecified /, partial_ordering v) noexcept; friend constexpr bool operator<=(/* unspecified */, partial_ordering v) noexcept; friend constexpr bool operator>=(/ unspecified /, partial_ordering v) noexcept; friend constexpr partial_ordering operator<=>(partial_ordering v, / unspecified /) noexcept; friend constexpr partial_ordering operator<=>(/ unspecified */, partial_ordering v) noexcept; };   // valid values' definitions inline constexpr partial_ordering partial_ordering::less(ord::less); inline constexpr partial_ordering partial_ordering::equivalent(eq::equivalent); inline constexpr partial_ordering partial_ordering::greater(ord::greater); inline constexpr partial_ordering partial_ordering::unordered(ncmp::unordered); }

[edit] Class std::weak_ordering

namespace std { class weak_ordering { int value; // exposition only   // exposition-only constructors constexpr explicit weak_ordering(eq v) noexcept : value(int(v)) {} // exposition only constexpr explicit weak_ordering(ord v) noexcept : value(int(v)) {} // exposition only   public: // valid values static const weak_ordering less; static const weak_ordering equivalent; static const weak_ordering greater;   // conversions constexpr operator partial_ordering() const noexcept;   // comparisons friend constexpr bool operator==(weak_ordering v, /* unspecified /) noexcept; friend constexpr bool operator==(weak_ordering v, weak_ordering w) noexcept = default; friend constexpr bool operator< (weak_ordering v, /* unspecified */) noexcept; friend constexpr bool operator> (weak_ordering v, / unspecified /) noexcept; friend constexpr bool operator<=(weak_ordering v, /* unspecified */) noexcept; friend constexpr bool operator>=(weak_ordering v, / unspecified /) noexcept; friend constexpr bool operator< (/* unspecified */, weak_ordering v) noexcept; friend constexpr bool operator> (/ unspecified /, weak_ordering v) noexcept; friend constexpr bool operator<=(/* unspecified */, weak_ordering v) noexcept; friend constexpr bool operator>=(/ unspecified /, weak_ordering v) noexcept; friend constexpr weak_ordering operator<=>(weak_ordering v, / unspecified /) noexcept; friend constexpr weak_ordering operator<=>(/ unspecified */, weak_ordering v) noexcept; };   // valid values' definitions inline constexpr weak_ordering weak_ordering::less(ord::less); inline constexpr weak_ordering weak_ordering::equivalent(eq::equivalent); inline constexpr weak_ordering weak_ordering::greater(ord::greater); }

[edit] Class std::strong_ordering

namespace std { class strong_ordering { int value; // exposition only   // exposition-only constructors constexpr explicit strong_ordering(eq v) noexcept : value(int(v)) {} // exposition only constexpr explicit strong_ordering(ord v) noexcept : value(int(v)) {} // exposition only   public: // valid values static const strong_ordering less; static const strong_ordering equal; static const strong_ordering equivalent; static const strong_ordering greater;   // conversions constexpr operator partial_ordering() const noexcept; constexpr operator weak_ordering() const noexcept;   // comparisons friend constexpr bool operator==(strong_ordering v, /* unspecified /) noexcept; friend constexpr bool operator==(strong_ordering v, strong_ordering w) noexcept = default; friend constexpr bool operator< (strong_ordering v, /* unspecified */) noexcept; friend constexpr bool operator> (strong_ordering v, / unspecified /) noexcept; friend constexpr bool operator<=(strong_ordering v, /* unspecified */) noexcept; friend constexpr bool operator>=(strong_ordering v, / unspecified /) noexcept; friend constexpr bool operator< (/* unspecified */, strong_ordering v) noexcept; friend constexpr bool operator> (/ unspecified /, strong_ordering v) noexcept; friend constexpr bool operator<=(/* unspecified */, strong_ordering v) noexcept; friend constexpr bool operator>=(/ unspecified /, strong_ordering v) noexcept; friend constexpr strong_ordering operator<=>(strong_ordering v, / unspecified /) noexcept; friend constexpr strong_ordering operator<=>(/ unspecified */, strong_ordering v) noexcept; };   // valid values' definitions inline constexpr strong_ordering strong_ordering::less(ord::less); inline constexpr strong_ordering strong_ordering::equal(eq::equal); inline constexpr strong_ordering strong_ordering::equivalent(eq::equivalent); inline constexpr strong_ordering strong_ordering::greater(ord::greater); }

[edit] Class std::compare_three_way

namespace std { struct compare_three_way { template<class T, class U> constexpr auto operator()(T&& t, U&& u) const;   using is_transparent = /* unspecified */; }; }

[edit] See also