如何定义两个相互依赖的类，最好是在同一个头文件中？

Question

So, I want something like:

class A{
B member;
};

class B{
A function();
};

No matter in which order I declare them, I get an incomplete type error (and I pretty much understand why). How can I solve this? I don't want to use pointers or to have the function defined outside the B class. Also, declaring them before as

class A; class B;

doesn't seem to work either.

Answer 1

No need for class definition when declare a function.

class A;
class B{
A function();
};
class A{
B member;
};

Answer 2

This order will work:

class A;

class B {
  A function();
};

class A {
  B member;
};