...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::proto::_::impl
// In header: <boost/proto/matches.hpp> template<typename Expr, typename State, typename Data> struct impl : proto::transform_impl<Expr, State, Data> { // types typedef Expr result_type; // public member functions Expr operator()(typename impl::expr_param, typename impl::state_param, typename impl::data_param) const; };