C++ function types

Question

I have a problem understanding function types (they appear e.g. as the Signature template parameter of a std::function):

typedef in         


        

Answer 1

In your case, std_fun_1 and std_fun_2 are identical objects with identical type signatures. They are both std::function, and can both hold function pointers or callable objects of type int(int).

pf is a pointer to int(int). That is, it serves the same basic purpose as std::function, but without the machinery of that class or support for instances of callable objects.

Similarly, std_fun_3 and std_fun_4 are identical objects with identical type signatures, and can both hold function pointers or callable objects of type int(int) const.

Also similarly, pfc is a function pointer of type int(int) const, and can hold pointers to functions of that type, but not instances of callable objects.

But f and fc are function declarations.

The line:

Signature fc;

Is identically equivalent to:

int fc(int) const;

Which is a declaration for a function named fc of type int(int) const.

There's nothing strange going on here. You've simply happened upon syntax you probably already understand, from a perspective you're not accustomed to.