How to make a circular dependency work?

[wolfv]

Is there a way to make this circular dependency work?

class A;	    //forward declare
class B
{
    private:
	A& refA;
    public:
	B(A& refA) : refA(refA) {}
};

class A
{
    private:
	B b;
    public:
	A(B b) : b(b) {}
};

int main()
{
	A a(b);     //error: 'b' was not declared in this scope
	B b(a);
}

The compile error is on line 20:
error: 'b' was not declared in this scope

How to pass b to constructor before b is instantiated?

Thank you.

[wolfv]

This solution compiles.
It initializes B::ptrA after both classes are instantiated.

class A;	        //forward declare
class B
{
    private:
	A* ptrA;
    public:
	void begin(A* a)
        {
            ptrA = a;
        }
};

class A
{
    private:
	B b;
    public:
	A(B b) : b(b) {}
};

int main()
{
	B b;
        A a(b);
        b.begin(&a);
}

The following code is similar; but it uses a reference refA in place of the pointer prtA. It does not compile:

class A;	        //forward declare
class B
{
    private:
	A& refA;
    public:
	void begin(A& a)
        {
            refA = a;   //error: invalid use of incomplete type 'class A'
        }
};

class A
{
    private:
	B b;
    public:
	A(B b) : b(b) {}
};

int main()
{
	B b;
        A a(b);
        b.begin(a);
}

Why does the reference not compile?

[cire]

Why does the reference not compile? Why does the reference not compile?

References must be initialized to refer to something. Here, you don't initialize the reference.

[wolfv]

Thanks cire.

[ne555]

> This solution compiles
that "solution" has different behaviour.
A(B b) : b(b) {} is doing a copy of the parameter. However at that point you have not yet bind the pointer.

You've got main::b.ptr that points to main::a
but main::a.b.ptr is uninitialized.


¿do you need main::b?

A a{ params };
A(params): b( params, this ){}