18 Concepts library [concepts]

18.7 Callable concepts [concepts.callable]

18.7.2 Concept invocable [concept.invocable]

The invocable concept specifies a relationship between a callable type ([func.def]) F and a set of argument types Args... which can be evaluated by the library function invoke ([func.invoke]).

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template<class F, class... Args>
  concept invocable = requires(F&& f, Args&&... args) {
    invoke(std::forward<F>(f), std::forward<Args>(args)...); // not required to be equality-preserving
  };

[Example 1:

A function that generates random numbers can model invocable, since the invoke function call expression is not required to be equality-preserving ([concepts.equality]).

— end example]