[Boost-users] iterator_facade and distance()

Hi, I am trying to implement an iterator using boost::iterator_facade. It works fine but it is very slow, I think because the distance() function takes lineair time as it is seems to be implemented in terms of increment(). I would like to implement the distance() function myself but I am not sure how. I tried to implement distance_to() like this: class const_data_stream_iterator : public boost::iterator_facade { public: typedef boost::iterator_facade facade_t; private: friend class boost::iterator_core_access; facade_t::difference_type difference_to(const_data_stream_iterator & to) const { ... } }; But this does not work. How can I do this? Thank you, Andrej