Hi. I have to say that I hate that the compiler associates a special bytecode for #class and that the VM don't even send the message. I want to be able to overwrite #class in a proxy for example, or to debug it. I did some benchmarks disabling such optimization by doing: (ParseNode classVarNamed: 'StdSelectors') removeKey: #class ifAbsent: []. Compiler recompileAll. And the difference is NOTHING in my tests (maybe I am doing something wrong). With Standard VM and #class optimization [SystemNavigation default allObjectsDo: [:each | each class]] timeToRun -> aprox 50 miliseconds With Standard VM and WITHOUT #class optimization [SystemNavigation default allObjectsDo: [:each | each class]] timeToRun -> aprox 60 miliseconds So...only 10 miliseconds more for asking the class to all the objects in the system.....(done in a PharoCore 1.3) With Cog VM and #class optimization [SystemNavigation default allObjectsDo: [:each | each class]] timeToRun -> aprox 13 miliseconds With Cog VM and WITHOUT #class optimization [SystemNavigation default allObjectsDo: [:each | each class]] timeToRun -> aprox 17 miliseconds So...only 5 miliseconds more for asking the class to all the objects in the system.....(done in a PharoCore 1.3) Considering (5 / 324535) asFloat 0,000015406... of overhead What do you think? Mariano