// In header: <boost/proto/functional/std/utility.hpp>

template<typename This, typename First, typename Second> 
struct result<This(First, Second)> {
  // types
  typedef std::pair<
        typename boost::remove_const<typename boost::remove_reference<First>::type>::type
      , typename boost::remove_const<typename boost::remove_reference<Second>::type>::type
    > type;
};