[Pharo-project] Fwd: [Pharo-users] another confusing result

[Mariano Martinez Peck]

---------- Forwarded message ----------
From: Larry White <ljw...@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...@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....@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

[Milan Mimica]

I would just remove the method. Probably the best fix ever.

--
Milan Mimica
http://sparklet.sf.net