...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::nullary_expr — A metafunction for generating nullary expression types, a grammar element for matching nullary expressions, and a PrimitiveTransform that returns the current expression unchanged.
// In header: <boost/proto/traits.hpp> template<typename Tag, typename T> struct nullary_expr : proto::transform< nullary_expr<Tag, T> > { // types typedef proto::expr< Tag, proto::term< T > > type; typedef proto::basic_expr< Tag, proto::term< T > > proto_grammar; // member classes/structs/unions template<typename Expr, typename State, typename Data> struct impl : proto::transform_impl< Expr, State, Data > { // types typedef Expr result_type; // public member functions Expr operator()(typename impl::expr_param, typename impl::state_param, typename impl::data_param) const; }; };