Here the original implementation, which Array inherits from SequenceableCollection: at: index ifAbsent: exceptionBlock "Answer the element at my position index. If I do not contain an element at index, answer the result of evaluating the argument, exceptionBlock." (index between: 1 and: self size) ifTrue: [^ self at: index]. ^ exceptionBlock value the thing is, that #at: primivite also doing a range checking and fails if index is invalid, so if index is valid, as result we performing a range checking twice instead of just once. Here the simple implementation how to make things faster: fat: index "Primitive. Assumes receiver is indexable. Answer the value of an indexable element in the receiver. Fail if the argument index is not an Integer or is out of bounds. Essential. See Object documentation whatIsAPrimitive. Read the class comment for a discussion about that the fact that the index can be a float." <primitive: 60> ^ #plopp fat: index ifAbsent: aBlock | x | x := (self fat: index). x == #plopp ifTrue: [ ^ aBlock value ]. ^ x And speedup is almost 2 times: [ 1000000 timesRepeat: [ #(1 2 4 5 56 67 67) at: 1 ifAbsent: nil ] ] timeToRun 39 [ 1000000 timesRepeat: [ #(1 2 4 5 56 67 67) at: 1 ifAbsent: nil ] ] timeToRun 20 Even when index is out of range, it is still much faster: [ 1000000 timesRepeat: [ #(1 2 4 5 56 67 67) at: 100 ifAbsent: nil ] ] timeToRun 35 [ 1000000 timesRepeat: [ #(1 2 4 5 56 67 67) fat: 100 ifAbsent: nil ] ] timeToRun 24 The problem, of course, that trick with #plopp is a dirty hack. Because if array include an #plopp object as element, it will report as it absent, instead of answering it. There is no way to ensure that any arbitrary object are never included as element in array, so this is no-go for generic replacement. But in controlled environment, when you know that none of arrays which you using with #fat:ifAbsent: will ever include #plopp (or pick your own unique object) it may be a good alternative. -- Best regards, Igor Stasenko.