Recursive Type Dependencies in C-CodePudding

#include <iostream>
#include <cstdlib>

class Egg;
class Chicken;

class Egg
{
public:
    Chicken *creator;
    Chicken getCreator()
    {
        if (!creator)
            return Chicken{};
        return *creator;
    }
};

class Chicken
{
public:
    Egg creator;
    Egg getCreator()
    {
        if (&creator == 0)
            return Egg{};
        return creator;
    }
};

void chicken_and_egg()
{

    Chicken chicken;
    Egg egg;
    chicken.creator = egg;
    egg.creator = &chicken;
    Egg e = chicken.getCreator();
    Chicken c = egg.getCreator();
    if (&(chicken.creator) == &(c.creator) && &(egg.creator) == &(e.creator))
    {
        using namespace std;
        cout << "the `Chicken and Egg' dilemma is solved!" << endl;
    }
}

int main()
{

    chicken_and_egg();

    return 0;
}

Does anybody know how to resolve the circular type dependencies in these two classes?

The creator in Egg class is reported to have incomplete type Chicken. I have tried to mess around with pointers but so far have found no clue.

CodePudding user response：

You need to define the member functions after the full definitions of the necessary classes have been seen. Example:

class Egg;
class Chicken;

class Egg {
public:
    Chicken* creator;
    Chicken getCreator(); // declaration only
};

class Chicken {
public:
    Egg creator;
    Egg getCreator(); // declaration only
};

// definitions:
Chicken Egg::getCreator() {
    if (!creator) return Chicken{};
    return *creator;
}

Egg Chicken::getCreator() {
    // strange comparison removed
    return creator;
}