synth-three-way , synth-three-way-result

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C++
Standard library
Customization point object (C++20)
Exposition-only entities
(C++11)
synth-three-way synth-three-way-result
(C++20) (C++20)
constexpr auto synth - three - way = /* see below */ ;
(1) (since C++20)
( exposition only* )
template < class T, class U = T >

using synth - three - way - result =

decltype ( synth - three - way ( std:: declval < T & > ( ) , std:: declval < U & > ( ) ) ) ;
(2) (since C++20)
( exposition only* )
1) A function object whose operator ( ) behaves as the synthesized three-way comparison function. Equivalent to: 
constexpr auto synth-three-way =
    []<class T, class U>(const T& t, const U& u)
        requires requires
        {
            { t < u } -> boolean-testable;
            { u < t } -> boolean-testable;
        }
    {
        if constexpr (std::three_way_comparable_with<T, U>)
            return t <=> u;
        else
        {
            if (t < u)
                return std::weak_ordering::less;
            if (u < t)
                return std::weak_ordering::greater;
            return std::weak_ordering::equivalent;
        }
    };
2) The return type of the operator ( ) of (1) ( synth-three-way ).

Parameters

t, u - the values to be compared

Return value

The compare result.

See also

(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values in the pair
(function template)
(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values in the tuple
(function template)
(C++11) (C++11) (removed in C++20) (C++11) (removed in C++20) (C++11) (removed in C++20) (C++11) (removed in C++20) (C++11) (removed in C++20) (C++20)
lexicographically compares the values of two array s
(function template)
(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values of two deque s
(function template)
(C++11) (C++11) (removed in C++20) (C++11) (removed in C++20) (C++11) (removed in C++20) (C++11) (removed in C++20) (C++11) (removed in C++20) (C++20)
lexicographically compares the values of two forward_list s
(function template)
(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values of two list s
(function template)
(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values of two vector s
(function template)
(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values of two map s
(function template)
(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values of two multimap s
(function template)
(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values of two set s
(function template)
(removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20)
lexicographically compares the values of two multiset s
(function template)
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