[Newbies] Deleting elements from a Collection while looping through
it
Jan Teske
jan.teske at student.hpi.uni-potsdam.de
Sat Dec 10 18:43:48 UTC 2011
Hey,
I have a question concerning the behavior of Collections in Squeak.
Recently I face a problem when trying to delete some elements from a set
during a 'do:' message.
Have a look at this sample method:
doFallForAllIn: aSet
aSet do:
[:block | block fall ifFalse: [aSet remove: block]]
It loops over a set of blocks and performs the fall message on each of
them. If a block is not falling I don't want it to be in aSet after the
function returned so I remove it from the set. Squeak doesn't seem to
like that since some rather strange error now occures: If a block is
removed from the set, the next block in the set will be left out from
looping... sometimes. Nearly all the time it works as exspected, only
sometimes a block is ignored. I couldn't find any pattern when this happens.
So my question is: Has anyone an explanation for this? Does the error
occure because the way I'm doing it is fundamentally wrong? Or am I just
overlooking something and it is possible to remove blocks from a
collection while looping over it?
Thanks in advance!
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