Question

My application has me calling a bunch of callbacks that need to know their last state, or the state of the last invocation. A simple instance is the time difference between two successive invocations.

I know that function objects in c++ are a generic way to do that. But I am a nOOb and not sure how to set this schema up. Any help or specific simple code examples will be much appreciated.

Answer 1

Just make a class that implements operator(). For instance,

class F {
    int state;
public:
    int operator()(/*any parameters would go here*/){
        return state++;
    }
    F() : state(0) {}
};

You can then create and instance which will be callable and retain state.

F f;
f(); //returns 0
f(); //returns 1