...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::_env::impl
// In header: <boost/proto/transform/env.hpp> struct impl : proto::transform_impl<Expr, State, Data> { // types typedef Data result_type; // public member functions result_type operator()(typename impl::expr_param, typename impl::state_param, typename impl::data_param) const; };