Hi, for tracing and logging one could easily write: foo ... Log enabled ifTrue: [ "do some tracing here" ]. ... but this always requires some message sends/checks if the debug mode is active. This is OK while debugging/tracing to find errors - but for runtime one whishes to have the best performance without any effect of tracing/debug code. Smalltalk/MT had a nice optimization feature that allowed to mix in debug code without additional overhead when in non-debug mode. If I remember correctly the basic idea was the following: there is a pool constant _DEBUG_INTERNAL that you compare to another pool constant TRUE (representing the value 1). So with an expresion like _DEBUG_INTERNAL == TRUE this ends up in 1 == 1 comparision which is always true if the pool constants/values have the same value of 1. A followup message send of #ifTrue: will always be executed - therefore means for the compiler to included the (debug) code: foo ... _DEBUG_INTERNAL == TRUE ifTrue: [ Processor outputDebugLine: 'Trace something' ]. ... So in this case (always true) this was optimized by the compiler to foo ... Processor outputDebugLine: 'Trace something' ... When _DEBUG_INTERNAL was set to FALSE (represented by value 0 as in C/C++) this ends up in 0 == 1 which is always false and will never be true. So a followup message send of #ifTrue: was optimized (removed as it was dead code and never reached). foo ... ... So depending on pool flag _DEBUG_INTERNAL and recompilation of (all) methods one could add debug/trace/logging code without runtime overhead. Yes this is very C language like to have conditional compilation - but very effective in keeping debug/tracing code influence low. I know we usually have the debugger in front of us - but sometimes a trace or log is required to see where code crashes. Think of a headless situation in a webserver or a small device like the pi where you want to reduce the performance overhead. This leads to several questions: - Is something like this feasible/already possible in Pharo? - Any pointers on how Opal does optimizations? Do we have similar optimizations (removing code that could not be reached) that could be used. - How do you usually deal with additional tracing code when you do not want to have too much runtime overhead. Thanks T.