---------- Forwarded message ---------- From: Larry White <ljw1001@gmail.com> Date: Tue, Jan 10, 2012 at 12:52 AM Subject: Re: [Pharo-users] another confusing result To: A friendly place where any question about pharo is welcome < pharo-users@lists.gforge.inria.fr> Thanks. I wonder if this method needs to stay the same for compatibility reasons or if it could be modified in Pharo to produce a less surprising result. In other words, is this a bug or a feature? On Mon, Jan 9, 2012 at 1:41 PM, Runar Jordahl <runar.jordahl@gmail.com>wrote:
Here is a copy of something I wrote about this earlier:
In Pharo 1.3, SequenceableCollection>>combinations:atATimeDo: will, for all combinations, send the same collection instance as argument for the block. Therefore, if you use this collection itself, you will be surprised:
|answer| answer := OrderedCollection new. #(a b c) combinations: 2 atATimeDo: [:each | answer add: each]. answer
Here I expect to end up with a collection looking like this: 1: #(#a #b) 2: #(#a #c) 3: #(#b #c)
But I end up with: 1: #(#c #c) 2: #(#c #c) 3: #(#c #c)
One fix is to change the client code to copy the argument for the block: |answer| answer := OrderedCollection new. #(a b c) combinations: 2 atATimeDo: [:each | answer add: each copy]. answer
Another solution is enhancing SequenceableCollection>>combinationsAt:in:after:do: to copy the collection: nn + 1 to: self size do: [ :index | aCollection at: jj put: (self at: index). jj = aCollection size ifTrue: [ aBlock value: aCollection copy ] ifFalse: [ self combinationsAt: jj + 1 in: aCollection after: index do: aBlock ] ]
Kind regards Runar Jordahl
-- Mariano http://marianopeck.wordpress.com