On 06/29/2011 12:07 AM, Holger Hans Peter Freyther wrote:
> - amortize their execution times. The default implementation
> - does nothing, so it is optimized out by the virtual machine
> - and so it loses very little on the performance side. Note
> - that descendants of Collection have to call it explicitly
> - since #do: is abstract in Collection."
> -
so this was not true about the VM/compiler? Was it true at some point?
It is true, but Gwen is looking at microoptimization. Also, originally
I was thinking of adding it only on top of O(n) or worse operations, but
this is not so since it's also in #first, #last, #at: etc. So,
#beConsistent imposes a fixed cost on frequently-read OrderedCollections.
In other words, with something like
- self beConsistent.
^lastIndex >= firstIndex
ifTrue: [self basicAt: lastIndex]
ifFalse: [SystemExceptions.IndexOutOfRange signalOn: self
withIndex: 0]
where you have four method calls (#at: itself and three primitives:
#beConsistent, #>=, #basicAt:), the single call to #beConsistent can
easily cost 5-10% or perhaps more.
Paolo
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