2017-04-12 13:17 GMT+02:00 Guillermo Polito <guillermopolito@gmail.com>:�� 1) each instance of A is becomed into its corresponding instance of A'�� 2) finally we become class A into A'�� �� �� This step will make that old instances of A now have:�� �� �� �� ��- the old format�� �� �� �� ��- but point to the new class Astep 1) ensures that there are no instances of class A anymore.Check following script:c1 := Class1 new.c2 := Class2 new.c1 becomeForward: c2.Class1 allInstances "=> #()".And full migration is executed in high priority uninterrupted process to ensure that between 1) and 2) nobody will instantiate Class1��