...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::result_of::left — A metafunction that returns the type of the left child of a binary Proto expression.
// In header: <boost/proto/traits.hpp> template<typename Expr> struct left : proto::result_of::child_c< Expr, 0 > { };