How can it be useful to overload the “function call” operator?

Question

I recently discovered that in C++ you can overload the \"function call\" operator, in a strange way in which you have to write two pair of parenthesis to do so:

Answer 1

A algorithm implemented using a template doesn't care whether the thing being called is a function or a functor, it cares about the syntax. Either standard ones (e.g. for_each()) or your own. And functors can have state, and do all kinds of things when they are called. Functions can only have state with a static local variable, or global variables.