Hi everyone, With Esteban, we bumped into a problem with anonymous subclasses and the slot class builder. The problem is that once an anonymous class is created is not possible to modify it. Here is the problem: For creating an anonymous class with the new class builder API you do something like: myAnonymousClass := AnonymousClassInstaller make: [ :classBuilder | classBuilder superclass: Object; name: #MyAnonymousClass; .... ] What happens is that the class builder asks the class installer if the class named #MyAnonymousClass exists or not to know if this a class to be created or to be modified. Here, the strategy of the anonymous class installer is to always answer no. So ok, now you have you're anonymous class. But what happens when you do something like: myAnonymousClass addInstVarNamed: #newIV Since the class has no clue of what class installer was used to create it, it instantiate a new one, and a PharoClassInstaller ! This new class installer then says to the class builder that there is no class named MyAnonymousClass so it creates it! And it install it in the system dictionary! And myAnonymousClass is not modified. So there is several problem here: - a class doesn't know which class installer was used to create it - even if the class would know that, the anonymous class installer would always say that it doesn't know it and a new class would be created So one possible solution for that is to have one class installer per environment (so add one iv in SystemDictionary right now), like that a class would know what class installer was used to create it. What would happen then is that you don't create anonymous classes anymore, that is to say a class not installed in any environment, but instead you create a class that exist in an environment separated from the system dictionary. What do you think?