Something

class parent{
public:
   int asdf;

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

int main(){
   A a;
   a.asdf = 2;
   A b = -a;
}