// In header: <boost/accumulators/statistics/sum.hpp>

template<typename Sample, typename Tag> 
struct sum_impl {
  // types
  typedef Sample result_type;

  // construct/copy/destruct
  template<typename Args> sum_impl(Args const &);

  // public member functions
  template<typename Args> void operator()(Args const &);
  result_type result(dont_care) const;
};