inherit from std::function, syntax and usage?

Question

I don't understand the syntax when a functor inherits from std::function:

class do_sth : public function< any_type (another_type) >
{
    bool operator() (string s) {...}
};

What should I use as any_type and another_type? And can you give me an example of a beneficial usage of inheriting from std::function since I haven't understood it yet?

Answer 1

You should use the return type of your operator () for any_type and the argument types for another_type. Then at least it fits.

But really, std::function is not meant to be inherited from, and doing so is probably a bad idea.