Hi When reading the code of readField: I have the impression that a part of this method should be moved to instructionStream. Same for writesField: Stef readsField: varIndex "Answer whether the receiver loads the instance variable indexed by the argument." "eem 5/24/2008 Rewritten to no longer assume the compiler uses the most compact encoding available (for EncoderForLongFormV3 support)." | varIndexCode scanner | varIndexCode := varIndex - 1. self isReturnField ifTrue: [^self returnField = varIndexCode]. ^(scanner := InstructionStream on: self) scanFor: [:b| b < 16 ifTrue: [b = varIndexCode] ifFalse: [b = 128 ifTrue: [scanner followingByte = varIndexCode and: [varIndexCode <= 63]] ifFalse: [b = 132 and: [(scanner followingByte between: 64 and: 95) and: [scanner thirdByte = varIndexCode]]]]]