How to empty a collection?
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I want to clear its contents (size goes back to zero), and can't seem to
find something like #clear or #empty. Cannot use a new collection as there are shared references to it. Thanks - Sophie _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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Some kind of facade that holds a collection, and replaces it with an empty one when you call #empty? You could forward all other calls.
On Feb 18, 2008 7:41 PM, itsme213 <[hidden email]> wrote: I want to clear its contents (size goes back to zero), and can't seem to _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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In reply to this post by Sophie424
I would do:
aCollection removeAll: aCollection Also, I have Aida in my image and I have: OrderedCollection>>removeAll "remove all elements quickly" self become: OrderedCollection new but not sure this way is good because of #become:. I don't know either if this will keep your references. hth Cédrick _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
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In reply to this post by Sophie424
On Feb 18, 2008, at 20:41 , itsme213 wrote: > I want to clear its contents (size goes back to zero), and can't > seem to > find something like #clear or #empty. Cannot use a new collection > as there > are shared references to it. myCollection removeAllSuchThat: [:each | true] - Bert - _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
RE: How to empty a collection?
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In reply to this post by Sophie424
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. Ron > -----Original Message----- > From: itsme213 > > I want to clear its contents (size goes back to zero), and can't seem to > find something like #clear or #empty. Cannot use a new collection as there > are shared references to it. > > Thanks - Sophie _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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Isn't Cedrick's aida solution going to be significantly faster?
On Feb 19, 2008 1:02 AM, Ron Teitelbaum <[hidden email]> wrote: Hi Sophie, _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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> Isn't Cedrick's aida solution going to be significantly faster?
> this is not mine :) butI'd interested to see if it's a good use of #become:... Does it keep references ? is it safe ? Thanks _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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My own testing suggests that references to the object remain in place. I would guess that that is the whole point of become.
On Feb 19, 2008 1:38 AM, cdrick <[hidden email]> wrote:
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My understanding as well is that this is the purpose of #become:, but
also that it is not very efficient in some versions of Smalltalk. If you are using an OrderedCollection, this is probably a reasonably efficient method as it doesn't need to search through the whole list every time it removes an element: removeAll [self notEmpty] whileTrue: [self removeLast] Brian. On Feb 18, 2008 6:42 PM, Marcin Tustin <[hidden email]> wrote: > My own testing suggests that references to the object remain in place. I > would guess that that is the whole point of become. > > > > On Feb 19, 2008 1:38 AM, cdrick <[hidden email]> wrote: > > > > > > Isn't Cedrick's aida solution going to be significantly faster? > > > > > > > this is not mine :) > > > > butI'd interested to see if it's a good use of #become:... Does it > > keep references ? is it safe ? > > > > Thanks > > > > > > > > _______________________________________________ > > Beginners mailing list > > [hidden email] > > http://lists.squeakfoundation.org/mailman/listinfo/beginners > > > > > _______________________________________________ > Beginners mailing list > [hidden email] > http://lists.squeakfoundation.org/mailman/listinfo/beginners > > Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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In reply to this post by Marcin Tustin
My understanding as well is that this is the purpose of #become:, but
also that it is not very efficient in some versions of Smalltalk. If you are using an OrderedCollection, this is probably a reasonably efficient method as it doesn't need to search through the whole list every time it removes an element: removeAll [self notEmpty] whileTrue: [self removeLast] Brian. On Feb 18, 2008 6:42 PM, Marcin Tustin <[hidden email]> wrote: > My own testing suggests that references to the object remain in place. I > would guess that that is the whole point of become. > > > > On Feb 19, 2008 1:38 AM, cdrick <[hidden email]> wrote: > > > > > > Isn't Cedrick's aida solution going to be significantly faster? > > > > > > > this is not mine :) > > > > butI'd interested to see if it's a good use of #become:... Does it > > keep references ? is it safe ? > > > > Thanks > > > > > > > > _______________________________________________ > > Beginners mailing list > > [hidden email] > > http://lists.squeakfoundation.org/mailman/listinfo/beginners > > > > > _______________________________________________ > Beginners mailing list > [hidden email] > http://lists.squeakfoundation.org/mailman/listinfo/beginners > > Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
RE: How to empty a collection?
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In reply to this post by Marcin Tustin
Hi Marcin,
I'm not a fan of using #become. I will use it for very specific behavior when I need to retain pointers to an object. For example for implementing a proxy. In that case become is a very useful tool. I think that #become is overkill for this situation, but I won't argue that it doesn't work. In most cases you have a well encapsulated collection. That collection is not referenced outside the object so you can just reinitialize your collection without #become. If it is complicated enough to worry about pointers I wouldn't use #become. Someone will get lost and miss your #become hidden inside #removeAll: . I'm not saying this will cause problems but I think I would rather work with the collection directly instead of using the #become. Also if you are working on a collection that is large enough to worry about performance then you are probably missing a database that would significantly improve your performance. Ron Teitelbaum ________________________________________ From: [hidden email] [mailto:[hidden email]] On Behalf Of Marcin Tustin Sent: Monday, February 18, 2008 8:43 PM To: A friendly place to get answers to even the most basic questions aboutSqueak. Subject: Re: [Newbies] How to empty a collection? My own testing suggests that references to the object remain in place. I would guess that that is the whole point of become. On Feb 19, 2008 1:38 AM, cdrick <[hidden email]> wrote: > Isn't Cedrick's aida solution going to be significantly faster? > this is not mine :) butI'd interested to see if it's a good use of #become:... Does it keep references ? is it safe ? Thanks _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
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In reply to this post by Marcin Tustin
On Tue, 19 Feb 2008 02:35:34 +0100, Marcin Tustin wrote:
> Isn't Cedrick's aida solution going to be significantly faster? No, solutions based on #become: are the slowest possible. The VM has to sweep the whole memory, for all variables in the system, to find all references during #become:, like this | oop | oop := self someObject. ["check+replace reference in variables of oop, then" oop := oop nextObject. oop = 0 ] whileFalse. Now think that you (and every other user of your software ;-) have an .image with 2-4gigs every time you use #become: ... If you want something faster, look at Bert's myCollection removeAllSuchThat: [:each | true] and try to make it faster but keep still it correct (old elements must be nil'ed). /Klaus > On Feb 19, 2008 1:02 AM, Ron Teitelbaum <[hidden email]> 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. >> >> Ron >> >> > -----Original Message----- >> > From: itsme213 >> > >> > I want to clear its contents (size goes back to zero), and can't seem >> to >> > find something like #clear or #empty. Cannot use a new collection as >> there >> > are shared references to it. >> > >> > Thanks - Sophie >> >> >> _______________________________________________ >> Beginners mailing list >> [hidden email] >> http://lists.squeakfoundation.org/mailman/listinfo/beginners >> _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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In reply to this post by Ron Teitelbaum
Hi! CCing squeak-dev because I would like to see this fixed. :) "Ron Teitelbaum" <[hidden email]> 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 _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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In reply to this post by Ron Teitelbaum
On Feb 19, 2008 2:29 AM, Ron Teitelbaum <[hidden email]> wrote: Hi Marcin, Re-initialize how? I can't see a way to run object initialisation over again on an existing object.
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Re: How to empty a collection?
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On Feb 19, 2008, at 10:53 , Marcin Tustin wrote:
> Re-initialize how? I can't see a way to run object initialisation > over again on an existing object. Everything in Smalltalk happens by sending a message. How was your object initialized? By sending a message. How can you initialize it again? Send the message again. Case in point - OrderedCollection. How is it initialized? Look at #new:. It sends #setCollection:. So send #setCollection: with a new Array and you're done. Well, of course you're not *supposed* to be doing this. But you could, and it would only be half-evil ;) - Bert - _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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In reply to this post by Göran Krampe
[hidden email] wrote:
> 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. A word of caution: identity should be preserved in the 'normal' case, replacing with another collection should be regarded as the exceptional case. Your assertion that "different objects should typically not share the same Collection." is only valid in limited cases. I'm talking from my experience with building mvc-based apps on VisualWorks. Code needs to be decoupled, ie 'model' objects and collections should not know about the UI's that are coupled to them, this is achieved with the various dependency mechanisms available in VW. Changing identity of the collections will break this paradigm big time (regardless of whether the dependents are managed in a global dictionary or by the collection itself). As to the implementation of #removeAll on non-growable collections: follow whatever pattern the squeak library uses for other messages that alter the size (#add:, #remove:,...). In VW the idiom is to call #shouldNotImplement. Cheers, R - _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
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In reply to this post by Brian M
>>>>> "Brian" == Brian Murphy-Dye <[hidden email]> writes:
Brian> My understanding as well is that this is the purpose of #become:, but Brian> also that it is not very efficient in some versions of Smalltalk. If Brian> you are using an OrderedCollection, this is probably a reasonably Brian> efficient method as it doesn't need to search through the whole list Brian> every time it removes an element: Brian> removeAll Brian> [self notEmpty] whileTrue: [self removeLast] What makes you think #removeLast doesn't need to search through the whole list in some kinds of OrderedCollection? You *do* have an implementation assumption there. I'd just do: removeAll self notEmpty ifTrue: [self become: self species new]. and let subclasses make it more efficient using implementation knowledge. -- Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095 <[hidden email]> <URL:http://www.stonehenge.com/merlyn/> Perl/Unix/security consulting, Technical writing, Comedy, etc. etc. See PerlTraining.Stonehenge.com for onsite and open-enrollment Perl training! _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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In reply to this post by Ron Teitelbaum
>
> 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. I forgot that in my first attemp (and I knew that !)... col := #(1 2 3) asOrderedCollection. col removeAll: col. ^col returns an OrderedCollection(2) col removeAll: col copy is ok. So, following Bert suggestion, would it be possible to change removeAll: from... removeAll: aCollection aCollection do: [:each | self remove: each]. ^ aCollection to removeAll: aCollection aCollection copy do: [:each | self remove: each]. ^ aCollection or removeAll: aCollection aCollection == self ifTrue: [aCollection copy do: [:each | self remove: each]] ifFalse: [aCollection do: [:each | self remove: each]]. ^ aCollection 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 _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
RE: How to empty a collection?
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Hi Cédrick,
I believe there is too little agreement to do very much. The suggestion you presented as Bert's suggestion was actually mine. So given the discussion that followed I think I would actually follow Bert's advice. aColl removeAllSuchThat: [:anElement| true]. But I suppose that is still following my own advice because removeAllSuchThat: aBlock "Evaluate aBlock for each element and remove all that elements from the receiver for that aBlock evaluates to true. Use a copy to enumerate collections whose order changes when an element is removed (i.e. Sets)." self copy do: [:each | (aBlock value: each) ifTrue: [self remove: each]] :) Ron Teitelbaum > -----Original Message----- > From: cdrick [mailto:[hidden email]]> > > > > 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. > > I forgot that in my first attemp (and I knew that !)... > > col := #(1 2 3) asOrderedCollection. > col removeAll: col. > ^col returns an OrderedCollection(2) > > col removeAll: col copy is ok. > > So, following Bert suggestion, would it be possible to change removeAll: > from... > > removeAll: aCollection > aCollection do: [:each | self remove: each]. > ^ aCollection > to > > removeAll: aCollection > aCollection copy do: [:each | self remove: each]. > ^ aCollection > or > > removeAll: aCollection > aCollection == self > ifTrue: [aCollection copy do: [:each | self remove: each]] > ifFalse: [aCollection do: [:each | self remove: each]]. > ^ aCollection > > 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 _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
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In reply to this post by cedreek
On Feb 19, 2008, at 16:06 , cdrick wrote:
> So, following Bert suggestion, would it be possible to change > removeAll: from... I'm pretty certain I did not suggest anything like this. Nothing is broken here, so let's not fix it. A new feature would be adding #removeAll, which sounds reasonable¹. - Bert - ¹I do smell a bit of premature optimization here, or does anyone have a really convincing use case? _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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