[Newbies] Re: How to empty a collection?

[Klaus D. Witzel]

On Tue, 19 Feb 2008 22:00:09 +0100, nicolas cellier wrote:

> Klaus D. Witzel a écrit :
>> On Tue, 19 Feb 2008 21:01:14 +0100, nicolas cellier wrote:
>>
>>> cdrick a écrit :
>>>>  or again
>>>> removeAll: aCollection
>>>>     aCollection == self
>>>>                 ifTrue: [self removeAll: aCollection copy]
>>>>                 ifFalse: [aCollection do: [:each | self remove:  
>>>> each]].
>>>>  Or maybe, if aCollection == self, a warning could be raised ?
>>>>  What do you think ?
>>>>  Cédrick
>>>>
>>>
>>> aCollection == self is not the only case that can fail.
>>> Imagine i pass a wrapper collection on self, like a MappedCollection.
>>>
>>> When i will change self with remove:, i will also change the argument  
>>> which is just a wrapper on self.
>>>
>>> Hope my explanations are not too much confusing...
>>  Let's see: "Remove each element of aCollection from the receiver. If  
>> successful for each, answer aCollection. Otherwise create an error  
>> notification."
>>  What mapping would *not* raise the error notification ;-)
>>
>
> My interpretation of the comment was rather for the case when we try to  
> remove an element which is not in the collection...
> But OK, I take it as is...
>
> However i can construct a test case that will not do what is expected  
> and will not raise a notification, wanna bet?

No, just let the next people who attempt to bring MappedCollection back to  
Squeak > 3.10 take care ;-)

BTW: do you have as much energy for fixing problems as you seem to have  
for imagine the currently non-existing ;-) This would help Squeak jump  
forward :)

> | collec1 collec2 |
> collec1 := OrderedCollection with: 'a' with: 'b' with: 'c'.
> collec2 := MappedCollection collection: collec1 map: (1 to: 2).
> 	"collec2 only map first two elements 'a' and 'b'"
> collec1 removeAll: collec2.
> 	"this should remove 'a' and 'b' from collec1"
> self assert: collec1 first = 'c'
> 	"too bad... it's 'b'"
>
>> BTW: MappedCollection does not exist in sq3.10-7159dev08.02.1.image ...
>>
>
> MappedCollection is just an example of possible wrapper collection, even  
> if there is none in core images nowadays, that's a classical pattern  
> which avoid copying for example.
>
> MappedCOllection is in 3.9 image.
>
>> /Klaus
>>
>>> Nicolas