Question about functors syntax

Hi, All !
I have a doubt regarding some syntax used in functors. For example, we have this:

[code]
class myFunctorClass
{
public:
myFunctorClass (int x) : _x( x ) {}

int operator() (int y) { return _x + y; }
private:
int _x;

}; [c/ode]

I know that the essential thing that makes one functor works is overloading the operator(), as shown in the code copied here above.
But my doubt is regarding the constructor syntax:

Code:

---

myFunctorClass (int x) : _x( x ) {}

---

The only syntax where I have seen that colon ( : ) in a constructor, is the syntax we use in a derived class to inherit from a base class whose constructor needs a parameter.
So, my question:
¿Which is the detailed meaning of this syntax?

Code:

---

myFunctorClass (int x) : _x( x ) {}

---

Thanks in advance!

It's called an initialisation list.
10.1 — Constructor initialization lists « Learn C++

If you are using C++11, you can use lambdas instead of functors. They are more convenient.

Hi !
Thanks a lot for your answers!
Elysia: I needed to know about that constructor syntax, even though another function (lambda, for example) may be better to use.