Enhancing SequenceableCollection>>combinationsAt:in:after:do:

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
blog.epigent.com

Thanks

can you propose some tests?
Did you sign the license agreement?

Stef

On Nov 2, 2011, at 7:57 PM, Runar Jordahl wrote: