template<class Owner>
class ref_counted
{
public:
	ref_counted()                       : m_ref_count(new unsigned long()) {}
	~ref_counted()                        {if(!(*m_ref_count)--) { delete m_ref_count; Owner::destroy(d); }

	ref_counted(const ref_counted& that)  {m_ref_count=that.m_ref_count; ++*m_ref_count;}
	void operator=(ref_counted that)      {std::swap(m_ref_count, that.m_ref_count);}

	bool is_last_referrer() const         {return *m_ref_count == 0;}
private:
	unsigned long*                        m_ref_count;
        typename Owner::data d;
};