...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::_env_var —
A primitive transform that returns the value associated with a particular Key
in the current transform environment.
// In header: <boost/proto/transform/env.hpp> template<typename Key> struct _env_var : proto::transform<_env_var<Key> > { // member classes/structs/unions struct impl : proto::transform_impl<Expr, State, Data> > { // types typedef typename proto::result_of::env_var<Data, Key>::type result_type; // public member functions result_type operator()(typename impl::expr_param, typename impl::state_param, typename impl::data_param) const; }; };