C++ Language/Std/Stl/CallableObjects/FunctionNameAsValue

The most simple form of a callable-object is the name of some existing function. If your software has already defined, then you might choose to define a callable-object as. In this case, the callable-object is a variable that can be manipulated like any other C++ variable. But the special thing about a callable-object is that it can be "invoked", either by a function-call-operator  or by.

Additional information about using a function name as a value (includes interactive examples)