Difference between revisions of "cpp/utility/compare/partial ordering"
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===Constants=== | ===Constants=== | ||
| − | The type {{tt|std:: | + | The type {{tt|std::partial_ordering}} has four valid values, implemented as const static data members of its type: |
{{dsc begin}} | {{dsc begin}} | ||
{{dsc hitem | Member type | Definition}} | {{dsc hitem | Member type | Definition}} | ||
Revision as of 14:57, 18 December 2017
| Defined in header <compare>
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| class partial_ordering; |
(since C++20) | |
The class type std::partial_ordering is the result type of a three-way comparison that
- admits all six relational operators (==, !=, <, <=, >, >=)
- does not imply substitutability: if a is equivalent to b, f(a) does not have to be equivalent to f(b)
- admits incomparable values: a < b, a == b, and a > b may all be false
Contents |
Constants
The type std::partial_ordering has four valid values, implemented as const static data members of its type:
| Member type | Definition |
| less(inline constexpr) [static] |
a valid value of the type std::partial_ordering indicating less-than (ordered before) relationship (public static member constant) |
| equivalent(inline constexpr) [static] |
a valid value of the type std::partial_ordering indicating equivalence (neither ordered before nor ordered after) (public static member constant) |
| greater(inline constexpr) [static] |
a valid value of the type std::partial_ordering indicating greater-than (ordered after) relationship (public static member constant) |
| unordered(inline constexpr) [static] |
a valid value of the type std::partial_ordering indicating relationship with an incomparable value (public static member constant) |
Conversions
std::partial_ordering is implicitly-convertible to std::weak_equality, while both std::strong_ordering and std::weak_ordering are implicitly-convertible to partial_ordering.
| operator weak_equality |
implicit conversion to std::weak_equality (function) |
std::strong_equality::operator weak_equality
| constexpr operator weak_equality() const noexcept; |
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Return value
std::weak_equality::equivalent if v is equivalent, std::weak_equality::nonequivalent if v is less, greater, or unordered.
Comparisons
Comparison operators are defined between values of this type and literal zero. This supports the expressions a <=> b == 0 or a <=> b < 0 that can be used to convert the result of a three-way comparison operator to a boolean relationship; see std::is_eq, std::is_lt, etc
| operator==operator!=operator<operator>operator<=operator>= |
compares with zero (function) |
operator==
| friend constexpr bool operator==(partial_ordering v, /*unspecified*/ u) noexcept; friend constexpr bool operator==(/*unspecified*/ u, partial_ordering v) noexcept; |
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Parameters
| v | - | a std::partial_ordering value to check
|
| u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true if v is equivalent, false if v is less, greater, or unordered
operator!=
| friend constexpr bool operator!=(partial_ordering v, /*unspecified*/ u) noexcept; friend constexpr bool operator!=(/*unspecified*/ u, partial_ordering v) noexcept; |
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Parameters
| v | - | a std::partial_ordering value to check
|
| u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true if v is unordered, less, or greater, and false if v is equivalent
operator<
| friend constexpr bool operator<(partial_ordering v, /*unspecified*/ u) noexcept; friend constexpr bool operator<(/*unspecified*/ u, partial_ordering v) noexcept; |
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Parameters
| v | - | a std::partial_ordering value to check
|
| u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true if v is less, and false if v is greater, equivalent, or unordered
operator<=
| friend constexpr bool operator<=(partial_ordering v, /*unspecified*/ u) noexcept; friend constexpr bool operator<=(/*unspecified*/ u, partial_ordering v) noexcept; |
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Parameters
| v | - | a std::partial_ordering value to check
|
| u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true if v is less or equivalent, and false if v is greater or unordered
operator>
| friend constexpr bool operator>(partial_ordering v, /*unspecified*/ u) noexcept; friend constexpr bool operator>(/*unspecified*/ u, partial_ordering v) noexcept; |
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Parameters
| v | - | a std::partial_ordering value to check
|
| u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true if v is greater, and false if v is less, equivalent, or unordered
operator>=
| friend constexpr bool operator>=(partial_ordering v, /*unspecified*/ u) noexcept; friend constexpr bool operator>=(/*unspecified*/ u, partial_ordering v) noexcept; |
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Parameters
| v | - | a std::partial_ordering value to check
|
| u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true if v is greater or equivalent, and false if v is less or unordered
Example
| This section is incomplete Reason: no example |
See also
| (C++20) |
the result type of 3-way comparison that supports all 6 operators and is substitutable (class) |
| (C++20) |
the result type of 3-way comparison that supports all 6 operators and is not substitutable (class) |
