I've really tried to make this work without using pointers. I want to create a shared class where two classes "see" each other and share this object. I wanted to initialize the shared object using an initializer list but I'm getting these errors.

error: field ‘shared_type’ has incomplete type ‘shared’
note: forward declaration of ‘class shared’
note: forward declaration of ‘class class_A’
note: forward declaration of ‘class class_B’

The first error doesn't make sense because the constructor for shared exists in shared.cpp.

I have tried declaring shared_type in class_A and class_B as const shared& shared_type; but that gave me an error saying that the lvalue is a const and the rvalue cannot be set to const, namely the value for the initializer. Is there anything else I could try without using pointers?

This is the complete code.

main.cpp

#include 
#include "include/class_A.h"
#include "include/class_B.h"

int main()
{

    return 0;
}

class_A.h

#ifndef CLASS_A_H
#define CLASS_A_H
//#include "shared.h"
class shared;
class class_A
{
    public:

        shared shared_type;

        class_A();
        ~class_A();

    protected:

    private:
};

#endif // CLASS_A_H

class_A.cpp

#include "class_A.h"

class_A::class_A() : shared_type()//this is the initializer for class_A
{
    //ctor
}

class_A::~class_A()
{
    //dtor
}

class_B.h

#ifndef CLASS_B_H
#define CLASS_B_H
//#include "shared.h"

class shared;
class class_B
{
    public:

        const shared& shared_type;
        class_B();
        ~class_B();

    protected:

    private:
};

#endif // CLASS_B_H

class_B.cpp

#include "class_B.h"

class_B::class_B() : shared_type()//this is the initializer for class_B
{
    //ctor
}

class_B::~class_B()
{
    //dtor
}

shared.h

#ifndef SHARED_H_
#define SHARED_H_

//#include "class_A.h"
//#include "class_B.h"

class class_A;
class class_B;

class shared
{
    private:

        class_A type_A;
        class_B type_B;

    public:

        shared();
        ~shared();
};
#endif

shared.cpp

#include "shared.h"

shared::shared(){}
shared::~shared(){}