18 Concepts library [concepts]

18.7 Callable concepts [concepts.callable]

template<class F, class... Args>
  concept regular_invocable = invocable<F, Args...>;

The invoke function call expression shall be equality-preserving ([concepts.equality]) and shall not modify the function object or the arguments.

[Note 1:

This requirement supersedes the annotation in the definition of invocable .

— end note]

[Example 1:

A random number generator does not model regular_invocable .

— end example]

[Note 2:

The distinction between invocable and regular_invocable is purely semantic.

— end note]