template<typename offset_functor, typename date_type> 
class date_itr : public boost::date_time::date_itr_base< date_type > {
public:
  // types
  typedef date_type::duration_type duration_type;

  // construct/copy/destruct
  date_itr(date_type, int = 1);

  // public member functions

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