// In header: <boost/accumulators/statistics_fwd.hpp>
template<typename N, typename Sample, typename Weight> 
struct weighted_moment_impl : public accumulator_base {
  // construct/copy/destruct
  template<typename Args> weighted_moment_impl(Args const &);
  // public member functions
   BOOST_MPL_ASSERT_RELATION(N::value, 0);
  template<typename Args> void operator()(Args const &);
  template<typename Args> result_type result(Args const &) const;
};