[cmp.weakord]

The weak_ordering type is typically used as the result type of a three-way comparison operator ([expr.spaceship]) for a type that admits all of the six two-way comparison operators ([expr.rel], [expr.eq]) and for which equality need not imply substitutability.

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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.