--- a/SocketAddress.st	Fri Feb 10 11:22:15 2017 +0100
+++ b/SocketAddress.st	Fri Feb 10 11:24:47 2017 +0100
@@ -540,6 +540,14 @@
     ^ self subclassResponsibility
 !
 
+isAbstract
+    "Return if this class is an abstract class.
+     True is returned here for myself only; false for subclasses.
+     Abstract subclasses must redefine this again."
+
+    ^ self == SocketAddress.
+!
+
 knownClassFromCode:code
     "this is a compatibility method;
      VW expects the internal unix codes here - however, in ST/X,