17 Language support library [support]

17.11 Comparisons [cmp]

17.11.2 Comparison category types [cmp.categories]

17.11.2.3 Class weak_­ordering [cmp.weakord]

1
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The weak_­ordering type is typically used as the result type of a three-way comparison operator that (a) admits all of the six two-way comparison operators ([expr.rel], [expr.eq]), and (b) does not imply substitutability.
namespace std { class weak_ordering { int value; // exposition only // exposition-only constructors 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(ord::equivalent); inline constexpr weak_ordering weak_ordering::greater(ord::greater); }
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constexpr operator partial_ordering() const noexcept;
2
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Returns: value == 0 ? partial_ordering::equivalent : value < 0 ? partial_ordering::less : partial_ordering::greater
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constexpr bool operator==(weak_ordering v, unspecified) noexcept; constexpr bool operator< (weak_ordering v, unspecified) noexcept; constexpr bool operator> (weak_ordering v, unspecified) noexcept; constexpr bool operator<=(weak_ordering v, unspecified) noexcept; constexpr bool operator>=(weak_ordering v, unspecified) noexcept;
3
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Returns: v.value @ 0 for operator@.
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constexpr bool operator< (unspecified, weak_ordering v) noexcept; constexpr bool operator> (unspecified, weak_ordering v) noexcept; constexpr bool operator<=(unspecified, weak_ordering v) noexcept; constexpr bool operator>=(unspecified, weak_ordering v) noexcept;
4
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Returns: 0 @ v.value for operator@.
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constexpr weak_ordering operator<=>(weak_ordering v, unspecified) noexcept;
5
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Returns: v.
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constexpr weak_ordering operator<=>(unspecified, weak_ordering v) noexcept;
6
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Returns: v < 0 ? weak_­ordering​::​greater : v > 0 ? weak_­ordering​::​less : v.