std::partial_order

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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.

See also

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