How to bind two classes that are referenced in a loop ？

[Stoneplay]

How to bind the following two classes in pybind11? B is declared first due to the reference in A and then is implemented behind A.

	class B;

	class A {
	public:
		A(B* b) : _b(b) {}
		~A() {}

	private:
		B* _b;
	};

	class B {
	public:
		B(A* a) : _a(a) {}
		~B() {}

	private:
		A* _a;
	};