// In header: <boost/accumulators/framework/accumulators/reference_accumulator.hpp>

template<typename Referent, typename Tag> 
struct reference_accumulator_impl :
  public boost::accumulators::accumulator_base
{
  // types
  typedef Referent & result_type;

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

  // public member functions
  result_type result(dont_care) const;
};