[Pharo-project] Stack should be reimplemented with Array

Eliot Miranda eliot.miranda at gmail.com
Thu Oct 14 13:51:31 EDT 2010

2010/10/14 jaayer <jaayer at zoho.com>

> There was a post on this list back in August complaining about Stack
> inheriting from LinkedList. There was some discussion, but apparently no
> resolution, as Stack still inherits from LinkedList in the Pharo 1.2 Core
> Image I just downloaded. Rather than reimplementing it to forward to a
> contained LinkedList, I think it should use an Array internally like
> OrderedCollection does. An Array-based implementation of Stack would be
> faster than one based on LinkedList due to the basic stack operations (push,
> pop and top) being able to rely more on primitives. This assumes that you
> know roughly how a big a stack you need; if you don't, reallocating the
> array and copying its contents over and over again will cost you, but this
> is an exceptional case;-- most stacks are small and when they aren't, the
> programmer usually has enough information to select a reasonable stack size.

*No*.  Stack and OrderedCollection differ *usefully*.  Adding an item to a
Stack is always O(1).  Adding an item to an OrderedCollection is O(N)
because when the array overflows a new one must be allocated and the old
objects copied to the new.  Why not apply your speedups to
OrderedCollection, or is that not possible?  If not possible, then come up
with a new name and add that.  Please /don't/ change Stack.

> Enclosed is a fileout of an Array-based Stack implementation. It trounces
> the LinkedList-based implementation easily, but more interestingly, it
> performs better than an OrderedCollection when used like a stack:
> Pushing is roughly ~30% faster:
> r1 :=[100000 timesRepeat: [
>                s := Stack new.
>                10 timesRepeat: [s push: #foo]]] timeToRun.
> r2 := [100000 timesRepeat: [
>                oc := OrderedCollection new.
>                10 timesRepeat: [oc addLast: #foo]]] timeToRun.
> 100 - ((r1 / r2) asFloat * 100).
> as is pushing + popping:
> r3 := [100000 timesRepeat: [
>                s := Stack new.
>                10 timesRepeat: [s push: #foo].
>                10 timesRepeat: [s pop]]] timeToRun.
> r4 := [100000 timesRepeat: [
>                oc := OrderedCollection new.
>                10 timesRepeat: [oc addLast: #foo].
>                10 timesRepeat: [oc removeLast]]] timeToRun.
> 100 - ((r3 / r4) asFloat * 100).
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