...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::nary_expr — A metafunction for generating n-ary expression types with a specified tag type,
a grammar element for matching n-ary expressions, and
a PrimitiveTransform
that dispatches to the
proto::pass_through<>
transform.
// In header: <boost/proto/traits.hpp> template<typename Tag, typename... A> struct nary_expr : proto::transform< nary_expr<Tag, A...> > { // types typedef proto::expr< Tag, proto::listN< A... > > type; typedef type proto_base_expr; // member classes/structs/unions template<typename Expr, typename State, typename Data> struct impl : proto::pass_through<nary_expr>::template impl<Expr, State, Data> { }; };
Use proto::nary_expr<proto::_, proto::vararg<proto::_> >
as a grammar element to match any n-ary expression; that is, any non-terminal.