相互关联的 C++ 类中多态性的最佳实践？

Question

I have a couple of interrelated classes that will be used by multiple different algorithms

Example:

struct B;

struct A {
    B* parent;
};

struct B {
    std::vector<A*> children;
};

Each algorithm may want to specialize these classes based on what they are doing with them, so presumably we they should derive from A and B

struct Aderived : A {...};
struct Bderived : B {...};

but methods in Aderived will want to treat parent as Bderived* (to access methods or members added by Bderived ) and Bderived will want to treat the elements of children as Aderived* .

1) Is there a good way for methods in Aderived and Bderived to avoid having to do static casts on parent and children every time they want to access a method of Bderived and Aderived , respectively.

2) How would you even get something like this to compile anyways since you can't forward declare that a class is derived from another...

struct Aderived : public A {
    int a;
    void x() { static_cast<Bderived*>(b)->b = 1; }   // ERROR
};

struct Bderived : public B {
    int b;
    void x() { static_cast<Aderived*>(avec.back())->a = 1; }
};

Answer 1

define A and B as templates:

template < class T1 >
struct A
{
    T1* parent;
};

template < class T2 >
struct B 
{
    std::vector < T2* > children;
};

and while inheritance go for:

struct Aderived : public A < Bderived >
{
  // ...
};

struct Bderived : public B < Aderived >
{
  //...
};

Answer 2

Just declare the member functions of A that cast B* to Bderived* and define them after defining Bderived :

struct Aderived : public A {
    int a;
    void x();
};

struct Bderived : public B {
    int b;
    void x() { static_cast<Aderived*>(avec.back())->a = 1; }
};

inline void Aderived::x() { static_cast<Bderived*>(b)->b = 1; }