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

 

哋它亢++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

Language support library

Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (哋它亢++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (哋它亢++17)

Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

Standard library

Exposition-only entities

decay-copy (哋它亢++11)

synth-three-waysynth-three-way-result (哋它亢++20)(哋它亢++20)

 

constexpr auto synth-three-way = /* see below */;	(1)	(since 哋它亢++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 哋它亢++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

operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values in the pair (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values in the tuple (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (哋它亢++11)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two arrays (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two deques (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (哋它亢++11)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++11)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two forward_lists (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two lists (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two vectors (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two maps (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two multimaps (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two sets (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(removed in 哋它亢++20)(哋它亢++20)	lexicographically compares the values of two multisets (function template)