let's have some fun and do Object subclass: #Behavior uses: TPureBehavior instanceVariableNames: 'superclass methodDict format layout' classVariableNames: 'ObsoleteSubclasses' poolDictionaries: '' category: 'Kernel-Classes' proceed over the several warnings not to change Behavior and BOOM! :D why would I do this? => we want first class layouts (most probably in 1.5) =============================================================================== StackInterpreter VMMaker-oscog-EstebanLorenzano.139 uuid: 5aa53979-d7d8-4ca3-91fe-cfc3b4109c33 =============================================================================== Recompiling Metaclass (2041/2046) 100% =============================================================================== Notice: Errors in script loaded from script.st =============================================================================== ==== Startup Error: MessageNotUnderstood: Dictionary>>asLowercase Dictionary(Object)>>doesNotUnderstand: #asLowercase ChangeSet>>noteClassStructure: ChangeSet>>changeClass:from: ChangeSet>>event: WeakMessageSend>>valueWithArguments: WeakActionSequenceTrappingErrors>>valueWithArguments:startingFrom: in Block: [answer := each valueWithArguments: anArray] BlockClosure>>on:do: WeakActionSequenceTrappingErrors>>valueWithArguments:startingFrom: WeakActionSequenceTrappingErrors>>valueWithArguments: SystemEventManager(Object)>>triggerEvent:withArguments: ... =============================================================================== CoInterpreter VMMaker-oscog-EstebanLorenzano.139 uuid: 5aa53979-d7d8-4ca3-91fe-cfc3b4109c33 =============================================================================== Recompiling Class class (924/2046) 45% =============================================================================== Notice: Errors in script loaded from script.st =============================================================================== ==== Startup Error: MessageNotUnderstood: ByteSymbol>>copyTraitExpression ByteSymbol(Object)>>doesNotUnderstand: #copyTraitExpression ClassBuilder>>mutate:to: in Block: [:oldSubclass | ... Array(SequenceableCollection)>>do: ClassBuilder>>mutate:to: ClassBuilder>>mutate:to: in Block: [:oldSubclass | ... Array(SequenceableCollection)>>do: ClassBuilder>>mutate:to: ClassBuilder>>mutate:to: in Block: [:oldSubclass | ... Array(SequenceableCollecti ... =============================================================================== now and then the CogVM crashes due to a SEGFAULT. Under one of the old Squeak VMs it compiles but depending on the VM version, has issues maintaining a sane state. So this is most certainly a VM issue and not a bug in the image side code. As far as I remember the CogVM opens a modified image without issues... best cami