template<class C>
class parent_op {
public:
   C parent::operator-(){
      C ret;
      ret.asdf *= -1;
      return ret;
   }
};

class actual_parent {
public:
   int asdf;
}

class A : public actual_parent, parent_op<A> {};
class B: public actual_parent, parent_op<B> {};
 
int main(){
   A a;
   a.asdf = 2;
   A b = -a;
}