#include <assert.h>
class parent {
public:

template<class C>
class operators {
public:
  operators() {
    const parent* parent_this = dynamic_cast<parent*>(dynamic_cast<C*>(this)); // make sure this is derived from parent as well                                                                                  
    assert(parent_this);
  }

  virtual ~operators() { };

  C operator-(){
    C ret;
    ret.asdf = static_cast<parent*>(static_cast<C*>(this))->asdf * -1;
    return ret;
  }
};

public:
  int asdf;
  virtual ~parent() { };

};

class A : public parent, public parent::operators<A> { public: virtual ~A() { }; };
class B : public parent::operators<A> { };