Prevent unused variable warning in presence of assertions.

include/zmq.hpp

@@ -40,6 +40,14 @@
 #   define ZMQ_HAS_RVALUE_REFS
 #endif
 
+// In order to prevent unused variable warnings when building in non-debug
+// mode use this macro to make assertions.
+#ifndef NDEBUG
+#   define ZMQ_ASSERT(expression) assert(expression)
+#else
+#   define ZMQ_ASSERT(expression) (expression)
+#endif
+
 namespace zmq
 {
 
@@ -118,7 +126,7 @@ namespace zmq
         inline ~message_t ()
         {
             int rc = zmq_msg_close (this);
-            assert (rc == 0);
+            ZMQ_ASSERT (rc == 0);
         }
 
         inline void rebuild ()
@@ -214,7 +222,7 @@ namespace zmq
             if (ptr == NULL)
                 return;
             int rc = zmq_term (ptr);
-            assert (rc == 0);
+            ZMQ_ASSERT (rc == 0);
         }
 
         //  Be careful with this, it's probably only useful for