DebugDelete 可调用对象模板

class DebugDelete {
public:
   DebugDelete(ostream &os = cerr)
      : m_os(os) {}
   template <typename T>
   void operator()(T *ptr) {
      m_os << "Delete the point" << endl;
      delete ptr;
   }
private:
   ostream &m_os;
};