template<class T>
struct wrap {};

struct connect_f {
  typedef void result_type;
  template<class Producer, class Self, class T>
  void operator()(Producer* producer, Self* self, const wrap<T>&) const {
      producer->connect(self->get_promise<T>());
  }
};

...

boost::mpl::for_each<consensus, wrap<mpl::_1> >(boost::bind(connect_f, &Producer, this, _1));