how to forward declare a class in a class ?

[OReubens]

If you have a class having a pointer to a not-yet defined class, you can forward declare that class. But how do you do this if the class is a class defined inside another class.

Below is a sample of the problem, this is what I'd like to get compiling but now it doesn't. the

// Helper class.  Basically a wrapped typed pointer.
template <typename Ty>
class ConstPtr
{
public:
	const  Ty* p;
	const Ty& operator()() { return *p; }
};

class A
{
public:
	class Item
	{
	public:
		const char*			szName;
		ConstPtr<B::Item>	b;	// <-- Problem
	};

	typedef std::tr1::array<Item,3> Array;
	static const Array All;
};

class B
{
public:
	class Item
	{
	public:
		const char*			szName;
		ConstPtr<A::Item>	a;
	};

	typedef std::tr1::array<Item,2> Array;
	static const Array All;
};

const A::Array A::All = 
{
	{
		{	"one",		&B::All._Elems[0], },
		{	"two",		&B::All._Elems[1], },
		{	"three",	&B::All._Elems[1], },
	}
};
const B::Array B::All = 
{
	{
		{	"red",		&A::All._Elems[0], },
		{	"blue",		&A::All._Elems[1], },
	}
};

Now the above is a simplified section of the problem, in reality I have several dozen of classes similar to A and B, with varying members in the Item classes.

I can't seem to figure out how to tell the compiler that at the definition of the A class that B::Item is a valid class and taking a pointer of it is ok.
if I change the ConstPtr<B::Item> to const void* the code compiles and "works" but I don't have a pointer of the right type in that case.