...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::transform::result<This(Expr, State)>
// In header: <boost/proto/transform/impl.hpp>
template<typename This, typename Expr, typename State>
struct result<This(Expr, State)> {
// types
typedef typename PrimitiveTransform::template impl< Expr, State, unspecified
>::result_type type;
};