[Newbies] How to empty a collection?

goran at krampe.se goran at krampe.se
Tue Feb 19 09:23:20 UTC 2008


CCing squeak-dev because I would like to see this fixed. :)

"Ron Teitelbaum" <Ron at USMedRec.com> wrote:
> Hi Sophie,
> aCollection copy do: [:anElement | 
> 	aCollection remove: anElement
> ].
> Why copy?  If you start removing items from the collection, increasing the
> index will cause you to skip elements.  

Because modifying the collection while iterating over the same is not
safe generally. The above idiom is "known" - but of course it sucks. :)

I advocated to add a #removeAll message in the protocol of Collection
and then implement it in subclasses using efficient variants a looooong
while back but it never got accepted. The climate today for such a
change is much more... "pragmatic" I think and hope. So we should simply
add it!

The *normal* way people usually do it thoiugh is to *not depend on the
identity* of the Collection - different objects should typically not
share the same Collection. And if you don't share - then the easy way
out is to just do:

	myCollection := OrderedCollection new "or whatever class you use"

...in order to empty it.

But in low level code it would be nice to have the #removeAll method
because it can be very efficiently implemented in different subclasses
and would avoid reallocations etc.

regards, Göran

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