std::compare_strong_order_fallback

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(C++20)(C++20)

strong_ordering

(C++20)

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(C++20)

partial_ordering

(C++20)

common_comparison_category

(C++20)

compare_three_way_result

(C++20)

(C++20)

(C++20)

(C++20)

(C++20)

compare_strong_order_fallback

(C++20)

compare_weak_order_fallback

(C++20)

compare_partial_order_fallback

(C++20)

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(C++20)(C++20)(C++20)

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Defined in header`<compare>`
inlinenamespace/* unspecified /{ inlineconstexpr/ unspecified / compare_strong_order_fallback=/ unspecified */; }		(since C++20)
Call signature
template<class T,class U> requires/* see below / constexprstd::strong_ordering compare_strong_order_fallback( T&& t, U&& u)noexcept(/ see below */);		(since C++20)

Performs three-way comparison onsubexpressionst andu and produces a result of typestd::strong_ordering, even if the operator<=> is unavailable.

Ifstd::decay_t<T> andstd::decay_t<U> are the same type,std::compare_strong_order_fallback(t, u) isexpression-equivalent to:

std::strong_order(t, u), if it is a well-formed expression;
otherwise,t== u? std::strong_ordering::equal:
t< u ? std::strong_ordering::less:
         std::strong_ordering::greater

if the expressionst== u andt< u are both well-formed and each ofdecltype(t== u) anddecltype(t< u) modelsboolean-testable, except thatt andu are evaluated only once.

In all other cases,std::compare_strong_order_fallback(t, u) is ill-formed, which can result insubstitution failure when it appears in the immediate context of a template instantiation.

Customization point objects

The namestd::compare_strong_order_fallback denotes acustomization point object, which is a constfunction object of aliteral semiregular class type. SeeCustomizationPointObject for details.