...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::reverse_fold_tree::impl
// In header: <boost/proto/transform/fold_tree.hpp> template<typename Expr, typename State, typename Data> struct impl : proto::reverse_fold<Sequence, State0, recurse_if_<typename Expr::proto_tag, Fun> > ::template impl<Expr, State, Data> { };