#include <map>
 
class A 
{
	public:
	virtual ~A();
		template <typename T> T * down()
		{
			return reinterpret_cast<T*>(this);
		}
 
};
 
template <int K>
class B : public A
{
public:
	static const int TYPE = K;
};
 
class C : public B<3>
{
 
};
 
 
class R
{
public:
 
	template <typename T> T * get()
	{
		auto i = _r.find(T::TYPE);
		if (i != _r.end())
		{
			return i->second->down<T>();
		}
		return 0;
	}
	std::map<int, A*> _r;
};
 
 
int main () 
{
	R r;
	r.get<C>();
}