class Top
{
};

class Middle : public Top
{
};

template< typename T >
class Tpl : public Top
{

};


class Visitor
{
  ~Visitor() {}

  virtual void visit( const Top& v );
  virtual void visit( const Middle& v );

  /* won't compile, so you cannot visit this class directly. sucks, eh?
  template< typename T >
  virtual void visit( const Tpl< T >& v );
  */
};

int
main()
{

  return 0;
}