An instance of jss::actor_ref holds a reference to
          an jss::actor
          instance.
        
namespace jss { class actor_ref { public: actor_ref(actor& a); template<typename Msg> void send(Msg&& msg) const; }; template<typename Msg> actor_ref const& operator<<(actor_ref const& ar,Msg msg); }
          #include <jss/actor.hpp>