boost::proto::integral_c — 一个 PrimitiveTransform,它返回指定的积分常量。
// In header: <boost/proto/transform/integral_c.hpp> template<typename T, T I> struct integral_c : proto::transform< integral_c< T, I > > { // member classes/structs/unions template<typename Expr, typename State, typename Data> struct impl : proto::transform_impl< Expr, State, Data > { // types typedef T result_type; // public member functions T operator()(typename impl::expr_param, typename impl::state_param, typename impl::data_param) const; }; };