template<typename date_type> 
class week_functor {
public:
  // types
  typedef date_type::duration_type duration_type;
  typedef date_type::calendar_type calendar_type;

  // construct/copy/destruct
  week_functor(int);

  // public member functions
  duration_type get_offset(const date_type &) const;
  duration_type get_neg_offset(const date_type &) const;
};