Question

First: I know my question is not about a parent class, but I don’t know how this structure is called and I thought parent would be the easiest to describe it.

I have two classes defined like this:

class class_a {
    void foo() {
        //stuff
    }
};

class class_b {
    class_a A;
    void foo() {
        //more stuff
    }
};

I want class_b::foo(); called when certain requirements are met in class_a::foo(); It’s possible to just set a variable in class_a and check for it in class_b::foo(); but I was wondering if there is a more elegant solution to this.

note: class_b is and can not be derived from class_a.

Answer 1

Not sure I completely understand what you are trying to do, a more concrete example would be helpful, but perhaps this does what you want:

class class_b;

class class_a {
    void foo(class_b* b);
};

class class_b {
    class_a A;
    void foo() {
        A.foo(this);
    }
    void foo_impl() {
        // stuff based on requirements in a::foo
    }
};

void class_a::foo(class_b* b) {
    //stuff
    if (conditionsMet()) {
        b->foo_impl();
    }
}