...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::_expr — A PrimitiveTransform that returns the current expression unmodified.
// In header: <boost/proto/transform/arg.hpp> struct _expr : proto::transform< _expr > { // 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; }; };
Example:
proto::terminal<int>::type i = {42}; proto::terminal<int>::type & j = proto::_expr()(i); assert( boost::addressof(i) == boost::addressof(j) );