--- a/extensions.st	Wed Dec 10 23:19:21 2014 +0100
+++ b/extensions.st	Mon Dec 15 00:16:44 2014 +0100
@@ -195,6 +195,21 @@
     "Created: / 30-09-2014 / 19:30:58 / Jakub Nesveda <nesvejak@fit.cvut.cz>"
 ! !
 
+!RBAbstractClass methodsFor:'accessing'!
+
+isAbstract: aBoolean
+    "see isAbstract"
+
+    self theMetaclass isNil ifTrue: [ 
+        self error: 'This class is not defined in the model.'
+    ].
+
+    self theMetaclass objectAttributeAt: #isAbstract put: aBoolean
+
+    "Created: / 14-12-2014 / 16:39:15 / Jakub Nesveda <nesvejak@fit.cvut.cz>"
+    "Modified: / 14-12-2014 / 18:12:03 / Jakub Nesveda <nesvejak@fit.cvut.cz>"
+! !
+
 !RBAbstractClass methodsFor:'autoload check'!
 
 isLoaded