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std::partial_order

Defined in header <compare> 
template< class T >
constexpr std::partial_ordering partial_order(const T& a, const T& b);
 (since C++20)

Compares two values using 3-way comparison and produces a result of type std::partial_ordering.

Specifically,

  • If the expression a <=> b is well-formed and its result is convertible to std::partial_ordering, returns that result.
  • Otherwise, if the expression a <=> b is well-formed, but its result is not convertible to std::partial_ordering, then the function is defined as deleted.
  • Otherwise, if the expression a <=> b is ill-formed, but the expressions a == b and a < b are both well-formed and convertible to bool,
    • if a == b is true, returns std::partial_ordering::equivalent
    • otherwise, if a < b is true, returns std::partial_ordering::less
    • otherwise, returns std::partial_ordering::greater
  • Otherwise, the function is defined as deleted.

Parameters

a, b - values to compare

Return value

A value of type std::partial_ordering, as described above.

Notes

Example

See also

(C++20)
 the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values
(class)
(C++20)
 performs 3-way comparison and produces a result of type std::strong_ordering
(function template)
(C++20)
 performs 3-way comparison and produces a result of type std::weak_ordering
(function template)
(C++20)
 performs 3-way comparison and produces a result of type std::weak_equality
(function template)

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