[Pharo-users] How to migrate an object to a subclass of its class but with new inst vars ?

Hi, i'm trying to migrate an object from a given class A to a subclass of A with new inst vars. Can't get it to work. I have a class and an instance of it, say: Object subclass: #A instanceVariableNames: '' |a| a := A new. A has no instance variables. Now i create a subclass B of A with a new inst var: A subclass: #B instanceVariableNames: 'x' I want to do the following: B adoptInstance: a It does'nt work, for what i understand it is because the format of the classes are different (B has an inst var and A has not). How can i make the a object become an instance of B (subclass of a's class), making a acquiring the new inst var x (and in more complex cases keeping its own previous inst vars) ? Steven.