How to empty a collection?
Locked
123
123
Re: How to empty a collection?
 
|
On Tue, 19 Feb 2008 16:06:50 +0100, cdrick wrote:
... > 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 ? Thumbs down, I do not want anybody copy a collection behind my back (however small or large it is) just because remove* has nothing to do with copy. > Cédrick _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
|
|
In reply to this post by Bert Freudenberg
>
> I'm pretty certain I did not suggest anything like this. Nothing is > broken here, so let's not fix it. My mistake, I'm sorry... It was Goran: "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!" I'm really tired today... ;) See you Cédrick _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
|
|
In reply to this post by Klaus D. Witzel
> >
> > Or maybe, if aCollection == self, a warning could be raised ? > > > > What do you think ? > > Thumbs down, I do not want anybody copy a collection behind my back > (however small or large it is) just because remove* has nothing to do with > copy. > Ok, I can understand. What about the error ? _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: Re: How to empty a collection?
|
|
On Tue, 19 Feb 2008 16:56:48 +0100, cdrick wrote:
>> > >> > Or maybe, if aCollection == self, a warning could be raised ? >> > >> > What do you think ? >> >> Thumbs down, I do not want anybody copy a collection behind my back >> (however small or large it is) just because remove* has nothing to do >> with copy. >> > Ok, I can understand. > What about the error ? This is a bug, Smalltalk cannot compromise its fundamental structures (#removeAll is ANSI). Enter the report if not already on mantis & attach your fix. /Klaus _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: Re: How to empty a collection?
|
|
On Tue, 19 Feb 2008 17:21:57 +0100, Klaus D. Witzel wrote:
> On Tue, 19 Feb 2008 16:56:48 +0100, cdrick wrote: > >>> > >>> > Or maybe, if aCollection == self, a warning could be raised ? >>> > >>> > What do you think ? >>> >>> Thumbs down, I do not want anybody copy a collection behind my back >>> (however small or large it is) just because remove* has nothing to do >>> with copy. >>> >> Ok, I can understand. >> What about the error ? > > This is a bug, Smalltalk cannot compromise its fundamental structures > (#removeAll is ANSI). Enter the report if not already on mantis & attach > your fix. Sorry, s/#removeAll /#removeAll: / > /Klaus > _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
|
|
In reply to this post by Randal L. Schwartz
[hidden email] (Randal L. Schwartz) wrote:
> >>>>> "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. I would never use become: in "regular code" like this. :) regards, Göran _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
|
|
In reply to this post by Reinout Heeck
Hi!
Reinout Heeck <[hidden email]> wrote: > [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, I agree. While I still think relying too much on identities is a dangerous practice. > 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. Well, I still stand by it as a general "nice rule". :) > 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. I know, I used VW back in the 2.5-3.x days and while I first thought the adapter-frenzy was cool I later also started thinking it was over-engineered as hell. ;) > 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). Yes, if your adapters/UI components etc cling onto the collections themselves, then yes, you will be bitten big time. I still think that paradigm is fishy - but again, I only presented the way people *typically* go about this thing - I still of course would like to preserve identity and introduce #removeAll. It is better in all respects. If the *intent* is to "remove all elements" - then the message should state exactly that intent. Doing stuff like "aColl copy do: [:each | aColl remove: each]" is just plain dumb and silly, though it would probably qualify as a default implementation in class Collection. :) regards, Göran _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Looking back... (was Re: How to empty a collection?)
|
|
Hi all!
Ok, since this was discussed AT PAINFULLY GREAT LENGTH back in aug/sept 2002 I just wanted to give you some reading on the subject at hand. Don't *ever* presume the issue you are bringing attention to hasn't been argued to death already :) :) Threads of discussions related to this from 2002: http://lists.squeakfoundation.org/pipermail/squeak-dev/2002-August/04315 7.html http://lists.squeakfoundation.org/pipermail/squeak-dev/2002-September/04 3926.html http://lists.squeakfoundation.org/pipermail/squeak-dev/2002-September/04 3928.html Especially Richard O Keefe did an awesome job back then IIRC. Now, if those threads will not exhaust you completely :) - then feel free to hack up a changeset that is a conclusion of all findings in there. :) regards, Göran _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
|
|
In reply to this post by Klaus D. Witzel
> >> >
I actually didn't meant it was a bug :) I need to be sharper with
> >> > Or maybe, if aCollection == self, a warning could be raised ? > >> > > >> > What do you think ? > >> > >> Thumbs down, I do not want anybody copy a collection behind my back > >> (however small or large it is) just because remove* has nothing to do > >> with copy. > >> > > Ok, I can understand. > > What about the error ? > > This is a bug, Smalltalk cannot compromise its fundamental structures > (#removeAll is ANSI). Enter the report if not already on mantis & attach > your fix. > my english... I meant raising an error message if self == aCollection ... Could it be a fix ? Because in a way, the behavior is not really an error, it's more a bad use because we know it's iterative and then, self and aCollection change in the same time... I hope you don't take my remarks, as "I want to change smalltalk"... I just want to understand it better ;) Cheers Cédrick ps: by the way, I'll open a bug report, as finally I think it's an error (arf....) because I shouldn't be aware removeAll is iterative....etc... so here is the bug report (http://bugs.squeak.org/view.php?id=6937). _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
|
|
In reply to this post by Göran Krampe
>>>>> "goran" == goran <[hidden email]> writes:
>> I'd just do: >> >> removeAll >> self notEmpty ifTrue: [self become: self species new]. >> >> and let subclasses make it more efficient using implementation knowledge. goran> I would never use become: in "regular code" like this. :) First, how "regular" is it if the method hasn't been missed by anyone in 27 years. :) Second, what are you objecting to? #become: is clearly a part of the image, and works fine. This code also cleans out a grown collection to be the smallest it possiby can become, where delete-one-at-a-time solutions don't. And, if there's a more efficient thing for subclasses, they can certainly override it. -- 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 |
Re: Looking back... (was Re: How to empty a collection?)
|
|
In reply to this post by Göran Krampe
Hi Goran!
I just want to point out that the long links in your mail were broken for me (although a little cut and paste fixed that). Perhaps a service like tinyURL would be useful when sending long links from the dark and distant past. I have noticed in this thread an undertone of "#become is the Devil's playground" Could someone succinctly explain to someone who is a coarse and styless programmer like myself why this is so, and when its use is justified? Thanks, John (keeping the newb in newbie for many years now) > Hi all! > > Ok, since this was discussed AT PAINFULLY GREAT LENGTH back in aug/sept > 2002 I just wanted to give you some reading on the subject at hand. > Don't *ever* presume the issue you are bringing attention to hasn't been > argued to death already :) :) > > Threads of discussions related to this from 2002: > > http://lists.squeakfoundation.org/pipermail/squeak-dev/2002-August/04315 > 7.html > http://lists.squeakfoundation.org/pipermail/squeak-dev/2002-September/04 > 3926.html > http://lists.squeakfoundation.org/pipermail/squeak-dev/2002-September/04 > 3928.html > <snip> > regards, Göran _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
|
|
In reply to this post by cedreek
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... Nicolas _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
|
|
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 ;-) BTW: MappedCollection does not exist in sq3.10-7159dev08.02.1.image ... /Klaus > Nicolas _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
|
|
In reply to this post by Randal L. Schwartz
On Feb 20, 2008 8:09 AM, Randal L. Schwartz <[hidden email]> wrote:
#become: and its friends are voodoo. Don't use them in your code unless you have absolutely no other option. It doesn't work fine. It breaks code that relies on hashes; specifically, a Dictionary elsewhere in your image can start acting screwy if you do a #become: variant that doesn't preserve an object's hash. See #becomeForward>>copyHash:. You would then also be relying on a Squeakish behaviour and your code would become less portable across Smalltalk dialects. They are also a fantastic way to introduce bugs of various sorts, and can even cause an image to crash (as in, stack trace and exit to the OS). Say, for example, that one of the arguments you pass is accidently nil, true or false? Your image would continue working... for a while. #become: and variants are also very slow and causes the equivalent of a full GC on every invocation. Gulik. -- http://people.squeakfoundation.org/person/mikevdg http://gulik.pbwiki.com/ _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: Looking back... (was Re: How to empty a collection?)
|
|
In reply to this post by John Foster-3
On Feb 20, 2008 8:47 AM, <[hidden email]> wrote: Hi Goran! Hi John the Newbie. It would be appreciated if you replied under a quoted message rather than above it. I've just sent an email in the original thread about this. It's use would only be justified if there are no other options. I've used it myself in my remote object architecture[1] for converting a message-capturing object proxy into the original object when an object is migrated between computers. My intention was to keep the remoteness of the objects involved as hidden as possible, making the use of #become: necessary. In retrospect, it was a big and dangerous time-waster. Many images died to bring me this information. Originally, the Collections framework in Squeak used become: to grow some collections. The blue book design of the Smalltalk VM[2] has an object lookup table where the implementation of #become: was very fast - switch a single pointer. The Squeak VM uses direct pointers between objects now, so the entire object memory needs to be scanned. [1] http://www.gulik.co.nz/dpon_design.pdf, http://www.squeaksource.com/DPON. [2] http://users.ipa.net/~dwighth/smalltalk/bluebook/bluebook_imp_toc.html Gulik. -- http://people.squeakfoundation.org/person/mikevdg http://gulik.pbwiki.com/ _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
|
|
In reply to this post by Klaus D. Witzel
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? | 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 _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
|
|
In reply to this post by Marcin Tustin
Hi,
This method is mine :) Ok, with a little IRC help from Radoslav Hodnicak. Why #become: ? As Marcin already suggested is a problem how to nil all existing elements in a collection, so to be garbage collected. This is specially problematic when collection has many elements and just doing an usual remove is too slow. In that case #become: is much faster, even that this method is slow on some dialects. Also, collection identity is preserved. But main point is that all elements are for sure GCed! Best regards Janko Marcin Tustin wrote: > My own testing suggests that references to the object remain in place. I > would guess that that is the whole point of become. cdrick 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 -- Janko Mivšek AIDA/Web Smalltalk Web Application Server http://www.aidaweb.si _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
|
|
In reply to this post by Nicolas Cellier-3
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 _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
|
|
In reply to this post by Randal L. Schwartz
[hidden email] (Randal L. Schwartz) wrote:
> >>>>> "goran" == goran <[hidden email]> writes: > >> I'd just do: > >> > >> removeAll > >> self notEmpty ifTrue: [self become: self species new]. > >> > >> and let subclasses make it more efficient using implementation knowledge. > > goran> I would never use become: in "regular code" like this. :) > > First, how "regular" is it if the method hasn't been missed by anyone > in 27 years. :) > > Second, what are you objecting to? #become: is clearly a part of the image, > and works fine. This code also cleans out a grown collection to be the > smallest it possiby can become, where delete-one-at-a-time solutions don't. > > And, if there's a more efficient thing for subclasses, they can certainly > override it. Yes, I probably agree it would be a nice default implementation. Modulo someone now telling us we missed something of course. :) regards, Göran _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: How to empty a collection?
|
|
In reply to this post by Klaus D. Witzel
Klaus D. Witzel a écrit :
> On Tue, 19 Feb 2008 22:00:09 +0100, nicolas cellier wrote: >> >> 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 ;-) > As a user of collection wrappers, proposed patch just hit the alarm buzzer my nervous brain is equipped with. But your position is wise. As long as a MappedCollection, lazy list or lazy collection (see these projects on SqueakSource) are all created under our control, we can manage... > 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 :) > That's precisely how i find and fix unknown bugs: Imagine how i could break current implementation. For this reason, most patches i proposed are minor. Hope a few are usefull, since adopted in 3.8.1, 3.9 and 3.10. Any minor contribution counts anyway :) Nicolas _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
«
Return to Squeak - Beginners
|
1 view|%1 views
| Free forum by Nabble | Edit this page |