Re: [Pharo-project] Stack should be reimplemented with Array
Eliot
There was a post on this list back in August complaining about Stack inheriting from LinkedList. There was some discussion, but apparently no resolution, as Stack still inherits from LinkedList in the Pharo 1.2 Core Image I just downloaded. Rather than reimplementing it to forward to a contained LinkedList, I think it should use an Array internally like OrderedCollection does. An Array-based implementation of Stack would be faster than one based on LinkedList due to the basic stack operations (push, pop and top) being able to rely more on primitives. This assumes that you know roughly how a big a stack you need; if you don't, reallocating the array and copying its contents over and over again will cost you, but this is an exceptional case;-- most stacks are small and when they aren't, the programmer usually has enough information to select a reasonable stack size.
*No*. Stack and OrderedCollection differ *usefully*. Adding an item to a Stack is always O(1). Adding an item to an OrderedCollection is O(N) because when the array overflows a new one must be allocated and the old objects copied to the new. Why not apply your speedups to OrderedCollection, or is that not possible? If not possible, then come up with a new name and add that. Please /don't/ change Stack.
I would really like not having Stack inheriting from LinkedList (I hate subclassing). Now from a VM point of view is there a constraint that Stack as to be a subclass of LList?
Enclosed is a fileout of an Array-based Stack implementation. It trounces the LinkedList-based implementation easily, but more interestingly, it performs better than an OrderedCollection when used like a stack:
Pushing is roughly ~30% faster: r1 :=[100000 timesRepeat: [ s := Stack new. 10 timesRepeat: [s push: #foo]]] timeToRun. r2 := [100000 timesRepeat: [ oc := OrderedCollection new. 10 timesRepeat: [oc addLast: #foo]]] timeToRun. 100 - ((r1 / r2) asFloat * 100).
as is pushing + popping: r3 := [100000 timesRepeat: [ s := Stack new. 10 timesRepeat: [s push: #foo]. 10 timesRepeat: [s pop]]] timeToRun. r4 := [100000 timesRepeat: [ oc := OrderedCollection new. 10 timesRepeat: [oc addLast: #foo]. 10 timesRepeat: [oc removeLast]]] timeToRun. 100 - ((r3 / r4) asFloat * 100). _______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
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On Mon, Oct 18, 2010 at 1:02 PM, Stéphane Ducasse <stephane.ducasse@inria.fr
wrote:
Eliot
There was a post on this list back in August complaining about Stack inheriting from LinkedList. There was some discussion, but apparently no resolution, as Stack still inherits from LinkedList in the Pharo 1.2 Core Image I just downloaded. Rather than reimplementing it to forward to a contained LinkedList, I think it should use an Array internally like OrderedCollection does. An Array-based implementation of Stack would be faster than one based on LinkedList due to the basic stack operations (push, pop and top) being able to rely more on primitives. This assumes that you know roughly how a big a stack you need; if you don't, reallocating the array and copying its contents over and over again will cost you, but this is an exceptional case;-- most stacks are small and when they aren't, the programmer usually has enough information to select a reasonable stack size.
*No*. Stack and OrderedCollection differ *usefully*. Adding an item to a Stack is always O(1). Adding an item to an OrderedCollection is O(N) because when the array overflows a new one must be allocated and the old objects copied to the new. Why not apply your speedups to OrderedCollection, or is that not possible? If not possible, then come up with a new name and add that. Please /don't/ change Stack.
I would really like not having Stack inheriting from LinkedList (I hate subclassing). Now from a VM point of view is there a constraint that Stack as to be a subclass of LList?
No. The VM doesn't know anything about Stack.
Enclosed is a fileout of an Array-based Stack implementation. It trounces
the LinkedList-based implementation easily, but more interestingly, it performs better than an OrderedCollection when used like a stack:
Pushing is roughly ~30% faster: r1 :=[100000 timesRepeat: [ s := Stack new. 10 timesRepeat: [s push: #foo]]] timeToRun. r2 := [100000 timesRepeat: [ oc := OrderedCollection new. 10 timesRepeat: [oc addLast: #foo]]] timeToRun. 100 - ((r1 / r2) asFloat * 100).
as is pushing + popping: r3 := [100000 timesRepeat: [ s := Stack new. 10 timesRepeat: [s push: #foo]. 10 timesRepeat: [s pop]]] timeToRun. r4 := [100000 timesRepeat: [ oc := OrderedCollection new. 10 timesRepeat: [oc addLast: #foo]. 10 timesRepeat: [oc removeLast]]] timeToRun. 100 - ((r3 / r4) asFloat * 100). _______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
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Stephane, i could say more: - i don't like how LinkedList implemented. I don't see why it should mimic things like #at: #at:put: at all.. IMO this protocol should be pruned from it, to not provoke uses which completely do not fit for given data structure. Removing/inserting into the middle of list is quite ineffective operation (O(n)), while inserting at the begginning/end of list is O(1). Lists are sequenceable.. but sequenceable ~~ indexable. Period. -- Best regards, Igor Stasenko AKA sig.
On Mon, 18 Oct 2010, Igor Stasenko wrote:
Stephane, i could say more: - i don't like how LinkedList implemented.
I don't see why it should mimic things like #at: #at:put: at all..
It's not mimicing those methods. A list usually support things like this, but the user should know the consequences.
IMO this protocol should be pruned from it, to not provoke uses which completely do not fit for given data structure.
I'm not sure if it's okay to remove features, because users lacking really basic CS knowledge may use them the wrong way.
Removing/inserting into the middle of list is quite ineffective operation (O(n)),
As long as you don't give away the link objects, it's O(n), otherwise it can be O(1).
while inserting at the begginning/end of list is O(1).
Lists are sequenceable.. but sequenceable ~~ indexable. Period.
Sequenceable is indexable, but good performance is not guaranteed. Levente
-- Best regards, Igor Stasenko AKA sig.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
On 19 October 2010 00:25, Levente Uzonyi <leves@elte.hu> wrote:
On Mon, 18 Oct 2010, Igor Stasenko wrote:
Stephane, i could say more: - i don't like how LinkedList implemented.
I don't see why it should mimic things like #at: #at:put: at all..
It's not mimicing those methods. A list usually support things like this, but the user should know the consequences.
The consequences of such approach is much more far-reaching: leads to bad design practices, crappy application performance, and then tons of bugs and workarounds.
IMO this protocol should be pruned from it, to not provoke uses which completely do not fit for given data structure.
I'm not sure if it's okay to remove features, because users lacking really basic CS knowledge may use them the wrong way.
Imo, we should prohibit this from the beginning. Standard, core classes should not contain an API, which could lead to careless, abusive programming techniques. IMO, a kernel APIs should serve not only as an implementation of basic system funcionality, it also must serve as guide, how to best use these facilities, so people will learn what is the right way to use it. We should teach users to use right tools for things they need.
Removing/inserting into the middle of list is quite ineffective operation (O(n)),
As long as you don't give away the link objects, it's O(n), otherwise it can be O(1).
giving away link objects... oh, that's the worst thing, which could possibly happen :)
while inserting at the begginning/end of list is O(1).
Lists are sequenceable.. but sequenceable ~~ indexable. Period.
Sequenceable is indexable, but good performance is not guaranteed.
Unless you representing an infinite collection(s). Streams are good example of sequenceable, however non-indexable containers.
Levente
-- Best regards, Igor Stasenko AKA sig.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- Best regards, Igor Stasenko AKA sig.
On Tue, 19 Oct 2010, Igor Stasenko wrote:
On 19 October 2010 00:25, Levente Uzonyi <leves@elte.hu> wrote:
On Mon, 18 Oct 2010, Igor Stasenko wrote:
Stephane, i could say more: - i don't like how LinkedList implemented.
I don't see why it should mimic things like #at: #at:put: at all..
It's not mimicing those methods. A list usually support things like this, but the user should know the consequences.
The consequences of such approach is much more far-reaching: leads to bad design practices, crappy application performance, and then tons of bugs and workarounds.
Are programmers idiots? If not, then we shouldn't treat them like idiots.
IMO this protocol should be pruned from it, to not provoke uses which completely do not fit for given data structure.
I'm not sure if it's okay to remove features, because users lacking really basic CS knowledge may use them the wrong way.
Imo, we should prohibit this from the beginning. Standard, core classes should not contain an API, which could lead to careless, abusive programming techniques.
So we should get rid of SortedCollection, remove #includes: #indexOf: from ArrayedCollections, get rid of OrderedCollection >> #remove:, etc. Am I right?
IMO, a kernel APIs should serve not only as an implementation of basic system funcionality, it also must serve as guide, how to best use these facilities, so people will learn what is the right way to use it.
That's right, but there's no need to remove useful features to achieve this.
We should teach users to use right tools for things they need.
Removing/inserting into the middle of list is quite ineffective operation (O(n)),
As long as you don't give away the link objects, it's O(n), otherwise it can be O(1).
giving away link objects... oh, that's the worst thing, which could possibly happen :)
No. It's the user's responsibility to use it wisely. If you don't need to access a internal nodes, just adding/removing elements to/from the list, then you probably shouldn't use a list at all.
while inserting at the begginning/end of list is O(1).
Lists are sequenceable.. but sequenceable ~~ indexable. Period.
Sequenceable is indexable, but good performance is not guaranteed.
Unless you representing an infinite collection(s). Streams are good example of sequenceable, however non-indexable containers.
Streams are more like external iterators, than containers IMHO. But you can get/set the position of most streams. Levente
Levente
-- Best regards, Igor Stasenko AKA sig.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- Best regards, Igor Stasenko AKA sig.
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On 19 October 2010 02:51, Levente Uzonyi <leves@elte.hu> wrote:
On Tue, 19 Oct 2010, Igor Stasenko wrote:
On 19 October 2010 00:25, Levente Uzonyi <leves@elte.hu> wrote:
On Mon, 18 Oct 2010, Igor Stasenko wrote:
Stephane, i could say more: - i don't like how LinkedList implemented.
I don't see why it should mimic things like #at: #at:put: at all..
It's not mimicing those methods. A list usually support things like this, but the user should know the consequences.
The consequences of such approach is much more far-reaching: leads to bad design practices, crappy application performance, and then tons of bugs and workarounds.
Are programmers idiots? If not, then we shouldn't treat them like idiots.
No, of course not. And that's why as non-idiot (i hope), i was wondering, what things like #at: #at:put: doing in classes like Stack, or LikedList. You know, its like you driving the car and along the road you see a beatiful park with pool and attractions for the kids to play to the right side, and a toxic waste dump to the left side of road.. And you keep driving, thinking about a diner and wife, which waits you at home, but at some moment your attention gets back to that place and you have a gut feeling that there was something wrong with a picture you just seen, and then you got it: they are close to each other, just across the road!
IMO this protocol should be pruned from it, to not provoke uses which completely do not fit for given data structure.
I'm not sure if it's okay to remove features, because users lacking really basic CS knowledge may use them the wrong way.
Imo, we should prohibit this from the beginning. Standard, core classes should not contain an API, which could lead to careless, abusive programming techniques.
So we should get rid of SortedCollection, remove #includes: #indexOf: from ArrayedCollections, get rid of OrderedCollection >> #remove:, etc. Am I right?
Roughly speaking, yes. But they are inherited.. this is a little another story. And should be handled in a way like Array>>add: does.
IMO, a kernel APIs should serve not only as an implementation of basic system funcionality, it also must serve as guide, how to best use these facilities, so people will learn what is the right way to use it.
That's right, but there's no need to remove useful features to achieve this.
you should convince me first, that things like LinkedList>>at: is userful.
We should teach users to use right tools for things they need.
Removing/inserting into the middle of list is quite ineffective operation (O(n)),
As long as you don't give away the link objects, it's O(n), otherwise it can be O(1).
giving away link objects... oh, that's the worst thing, which could possibly happen :)
No. It's the user's responsibility to use it wisely. If you don't need to access a internal nodes, just adding/removing elements to/from the list, then you probably shouldn't use a list at all.
I prefer making own lists and own classes for list items, because implementation of LinkedList raising many questions starting from being optimal, and up to concerns i presented above.
while inserting at the begginning/end of list is O(1).
Lists are sequenceable.. but sequenceable ~~ indexable. Period.
Sequenceable is indexable, but good performance is not guaranteed.
Unless you representing an infinite collection(s). Streams are good example of sequenceable, however non-indexable containers.
Streams are more like external iterators, than containers IMHO. But you can get/set the position of most streams.
Levente
Levente
-- Best regards, Igor Stasenko AKA sig.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- Best regards, Igor Stasenko AKA sig.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- Best regards, Igor Stasenko AKA sig.
On Tue, 19 Oct 2010, Igor Stasenko wrote:
On 19 October 2010 02:51, Levente Uzonyi <leves@elte.hu> wrote:
On Tue, 19 Oct 2010, Igor Stasenko wrote:
On 19 October 2010 00:25, Levente Uzonyi <leves@elte.hu> wrote:
On Mon, 18 Oct 2010, Igor Stasenko wrote:
Stephane, i could say more: - i don't like how LinkedList implemented.
I don't see why it should mimic things like #at: #at:put: at all..
It's not mimicing those methods. A list usually support things like this, but the user should know the consequences.
The consequences of such approach is much more far-reaching: leads to bad design practices, crappy application performance, and then tons of bugs and workarounds.
Are programmers idiots? If not, then we shouldn't treat them like idiots.
No, of course not. And that's why as non-idiot (i hope), i was wondering, what things like #at: #at:put: doing in classes like Stack, or LikedList.
Okay, it's not nice if a Stack allows indexing, but most linked list implementations support it.
You know, its like you driving the car and along the road you see a beatiful park with pool and attractions for the kids to play to the right side, and a toxic waste dump to the left side of road.. And you keep driving, thinking about a diner and wife, which waits you at home, but at some moment your attention gets back to that place and you have a gut feeling that there was something wrong with a picture you just seen, and then you got it: they are close to each other, just across the road!
IMO this protocol should be pruned from it, to not provoke uses which completely do not fit for given data structure.
I'm not sure if it's okay to remove features, because users lacking really basic CS knowledge may use them the wrong way.
Imo, we should prohibit this from the beginning. Standard, core classes should not contain an API, which could lead to careless, abusive programming techniques.
So we should get rid of SortedCollection, remove #includes: #indexOf: from ArrayedCollections, get rid of OrderedCollection >> #remove:, etc. Am I right?
Roughly speaking, yes. But they are inherited.. this is a little another story. And should be handled in a way like Array>>add: does.
Array >> #add: is different, because Arrays are not resizable. You could say that one could use #become: to grow the array, but then I'd say that following your suggestions we have to remove #become: from the system, because it's slow and people may use it to write slow code.
IMO, a kernel APIs should serve not only as an implementation of basic system funcionality, it also must serve as guide, how to best use these facilities, so people will learn what is the right way to use it.
That's right, but there's no need to remove useful features to achieve this.
you should convince me first, that things like LinkedList>>at: is userful.
Ok. Here's an example: What happens if you remove OrderedCollection >> #remove: from the system? People will write code like this (or worse): gotIt := false. 1 to: o size do: [ :index | gotIt ifTrue: [ o at: index - 1 put: (o at: index) ] ifFalse: [ (o at: index) = myObject ifTrue: [ gotIt := true ] ]. gotIt ifTrue: [ o removeLast ]. This kind of code is a lot worse than using #remove:, because it's harder to understand, harder to debug, really easy to mess up. And it will be reimplemented several times. Levente
We should teach users to use right tools for things they need.
Removing/inserting into the middle of list is quite ineffective operation (O(n)),
As long as you don't give away the link objects, it's O(n), otherwise it can be O(1).
giving away link objects... oh, that's the worst thing, which could possibly happen :)
No. It's the user's responsibility to use it wisely. If you don't need to access a internal nodes, just adding/removing elements to/from the list, then you probably shouldn't use a list at all.
I prefer making own lists and own classes for list items, because implementation of LinkedList raising many questions starting from being optimal, and up to concerns i presented above.
while inserting at the begginning/end of list is O(1).
Lists are sequenceable.. but sequenceable ~~ indexable. Period.
Sequenceable is indexable, but good performance is not guaranteed.
Unless you representing an infinite collection(s). Streams are good example of sequenceable, however non-indexable containers.
Streams are more like external iterators, than containers IMHO. But you can get/set the position of most streams.
Levente
Levente
-- Best regards, Igor Stasenko AKA sig.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- Best regards, Igor Stasenko AKA sig.
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
_______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
-- Best regards, Igor Stasenko AKA sig.
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participants (4)
-
Eliot Miranda -
Igor Stasenko -
Levente Uzonyi -
Stéphane Ducasse