Hi,
the code of primitive 60 seems to be assuming that the method has exactly one argument, ignoring the actual number of arguments. This seems to be an unnecessary restriction, which makes it cumbersome/impossible to use it in methods which have more arguments, like #at:ifAbsent:.
Since the primitive uses two objects from the top of the stack, it's possible to write a hackish method to see the potential benefits:
ifAbsent: aBlock receiver: receiver at: index
<primitive: 60> ^aBlock value
The primitive will treat the variable receiver as the receiver, and index as the index. The real receiver is not used at all.
This method performs 37% better than #at:ifAbsent for the case where the index is valid.
Does it have any benefits not taking the actual number of arguments into account in this primitive?
Cheers, Levente