keep _monitor_socket as private member

Author: dietelTiMaMi

tests/monitor.cpp

@@ -172,7 +172,7 @@ TEST_CASE("poll monitor events using active poller", "[monitor]")
         void addToPoller(zmq::active_poller_t &inActivePoller)
         {
             inActivePoller.add(
-              _monitor_socket, zmq::event_flags::pollin,
+              monitor_socket(), zmq::event_flags::pollin,
               [&](zmq::event_flags ef) { process_event(static_cast<short>(ef)); });
         }
 

zmq.hpp

@@ -2589,13 +2589,14 @@ class monitor_t
         return true;
     }
 
-    socket_t _monitor_socket;
+    socket_ref monitor_socket() {return _monitor_socket;}
 
   private:
     monitor_t(const monitor_t &) ZMQ_DELETED_FUNCTION;
     void operator=(const monitor_t &) ZMQ_DELETED_FUNCTION;
 
     socket_ref _socket;
+    socket_t _monitor_socket;
 
     void close() ZMQ_NOTHROW
     {