17 Language support library [support]

17.11 Comparisons [cmp]

17.11.2 Comparison category types [cmp.categories]

17.11.2.4 Class strong_­ordering [cmp.strongord]

1
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The strong_­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 imply substitutability.
namespace std { class strong_ordering { int value; // exposition only // exposition-only constructors 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(ord::equal); inline constexpr strong_ordering strong_ordering::equivalent(ord::equivalent); inline constexpr strong_ordering strong_ordering::greater(ord::greater); }
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constexpr operator partial_ordering() const noexcept;
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Returns: value == 0 ? partial_ordering::equivalent : value < 0 ? partial_ordering::less : partial_ordering::greater
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constexpr operator weak_ordering() const noexcept;
3
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Returns: value == 0 ? weak_ordering::equivalent : value < 0 ? weak_ordering::less : weak_ordering::greater
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constexpr bool operator==(strong_ordering v, unspecified) noexcept; constexpr bool operator< (strong_ordering v, unspecified) noexcept; constexpr bool operator> (strong_ordering v, unspecified) noexcept; constexpr bool operator<=(strong_ordering v, unspecified) noexcept; constexpr bool operator>=(strong_ordering v, unspecified) noexcept;
4
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Returns: v.value @ 0 for operator@.
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constexpr bool operator< (unspecified, strong_ordering v) noexcept; constexpr bool operator> (unspecified, strong_ordering v) noexcept; constexpr bool operator<=(unspecified, strong_ordering v) noexcept; constexpr bool operator>=(unspecified, strong_ordering v) noexcept;
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Returns: 0 @ v.value for operator@.
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constexpr strong_ordering operator<=>(strong_ordering v, unspecified) noexcept;
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Returns: v.
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constexpr strong_ordering operator<=>(unspecified, strong_ordering v) noexcept;
7
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Returns: v < 0 ? strong_­ordering​::​greater : v > 0 ? strong_­ordering​::​less : v.