July 2018 - Pharo-users - lists.pharo.org

Re: [Pharo-users] a basic hash question

by werner kassens

Hi, thank you all for your answers. CÃ©drick BÃ©ler wrote: > But it raises the question if : > (1 to:4)hash = #(1 2 3 4)hash should return true instead ?? principally yes, but it would slow down the Interval>>hash implementation considerably. id guess one would first make SequentialCollection>>hash a bit faster & shorter or one could very fast get a memory overflow. i mean the trick with Intervals is not so much (1to:4), but (-100000000000 to: 100000000000) which doesnt use any space and time. jgfoster wrote: > In GemStone the objects are not > equivalent (Iâm not arguing that this is right, just that it avoids the > problem you identify). i see, yes, it can happen that hash has its own idea what equivalence _really means. > I wonder what would happen if the hash comparison were added to the > equivalence operator (#â=â)! you probably mean something like this: #= ^(doWhatYouveDoneBefore)and:[self hash = object hash] of course that would eliminate the problem but it would need to be implemented everywhere. if not, #= could become not symmetric which produces the same problems (actually i stumbled upon this question because i implemented #= for a subobject of Array and gave it the species Array, problematic because with my implementation it opened the possibility of myObject~=anArray but anArray=myObject). actually #= in pharo is symmetric (and transitive, which also is necessary for hash to work) because it is more or less carefully designed , the symmetry is not somehow automatically incorporated in the language, and as i noticed its not too difficult to break that symmetry with ones own objects <stupid grin> On 07/30/2018 05:27 PM, Henrik Sperre Johansen wrote: > +1, this is a bug. > Either Interval >> #hash needs to change*, or the equivalency be broken**. > > Fun fact: > #(1 2 3 4) = #[1 2 3 4] false > You'd think they might be more similar than an Interval and an Array, or a > LinkedList containing ValueLinks and an Interval, but no ;) <g> i guess it is difficult to juggle & balance everything between all the different kinds of collections. thanks again folks werner

July 30, 2018

Re: [Pharo-users] a basic hash question

by Henrik Sperre Johansen

jgfoster wrote > Werner, > > I would say that you are right, this is a problem. A (not un-common) > source of subtle bugs in Smalltalk is missing this rule that equivalent > objects must have the same hash. In GemStone the objects are not > equivalent (Iâm not arguing that this is right, just that it avoids the > problem you identify). > > I wonder what would happen if the hash comparison were added to the > equivalence operator (#â=â)! > > James > >> On Jul 30, 2018, at 5:07 AM, werner kassens < > wkassens@ > > wrote: >> >> Hi, >> i guess i can subsume almost everything i know about hashes in one >> sentence: >> it is my understanding that two objects that are equal (obj1=obj2. >> -->true) have to have the same hash value (which is used for some >> collection types), whereas objects where obj1=obj2 returns false should >> have different hash values although it may happen that they have the >> same one. >> >> now here things don't turn out exactly like that: >> (1 to:4) = #(1 2 3 4). "true" >> (1 to:4)hash = #(1 2 3 4)hash. "false" >> well ok, actually these results make - pfffh, in a certain way - sense >> to me, but i wonder what arguments the people in the know would use to >> defend that result, if i would have another opinion? >> werner >> >> >> +1, this is a bug. Either Interval >> #hash needs to change*, or the equivalency be broken**. Fun fact: #(1 2 3 4) = #[1 2 3 4] false You'd think they might be more similar than an Interval and an Array, or a LinkedList containing ValueLinks and an Interval, but no ;) Cheers, Henry *Interval >> hash "Hash is reimplemented because = is implemented. Since we are equivalent to other collections of our species, we must also hash equivalently" | hash | hash := self species hash. start to: stop by: step do: [:element | hash := (hash + element hash) hashMultiply]. ^hash **both ways, which is challenging, if one neither wants to: - change species of Interval (which has bad consequences) - add hash comparison to sequenceablecollection = (which slows it down even further) -- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html

July 30, 2018

Re: [Pharo-users] transactions on pharo objects

by Esteban A. Maringolo

El lun., 30 jul. 2018 a las 11:03, Sean P. DeNigris (<sean(a)clipperadams.com>) escribiÃ³: > > Peter UhnÃ¡k wrote > > is there some library or approach how to do transactionsâ¦ directly in > > memory on Pharo > > objects > > Magritte? It uses the Memento pattern to verify all changes before > committing to real object. But you need Magritte, and define descriptions, and references, and access the objects via Magritte Accessors, etc. I think that works for an UI of a somehow limited form, but not as a general purpose (as I guess Peter is looking for). Also for forms, but without metadata, Dolphin used a "BufferedModel" object, which means that if you have an MVP/MVC, instead of using your original model, you work on this "buffer", which internally has the original and a copy, and all messages are sent to the copy and once you "apply" the changes they are applied back to the original model, and if you don't apply, the copy is discarded and the original model left unmodified. But again, I guess Peter is looking for something else. Regards!

July 30, 2018

Re: [Pharo-users] transactions on pharo objects

by Sean P. DeNigris

Peter UhnÃ¡k wrote > is there some library or approach how to do transactionsâ¦ directly in > memory on Pharo > objects Magritte? It uses the Memento pattern to verify all changes before committing to real object. ----- Cheers, Sean -- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html

July 30, 2018

Re: [Pharo-users] transactions on pharo objects

by Serge Stinckwich

Maybe you can have a look to this paper : https://www.sciencedirect.com/science/article/pii/S1477842408000237 On Mon, Jul 30, 2018 at 2:17 PM Peter UhnÃ¡k <i.uhnak(a)gmail.com> wrote: > Hi, > > is there some library or approach how to do transactions in pharo? > And I don't mean database transactions, but directly in memory on Pharo > objects... e.g. > > p := Person new. > > transaction do: [ > p name: 'Nobody'. > p age: 70. > ] on: Error do: [ > transaction rollback. > ]. > > self assert: p name equals: 'Nobody'. > self assert: p age equals: 70. > > transaction do: [ > p name: 'Somebody'. > p age: 1 / 0. > ] on: Error do: [ > transaction rollback. > ]. > > self assert: p name equals: 'Nobody'. > self assert: p age equals: 70. > > Any pointers appreciated. > > Thanks, > Peter > -- Serge Stinckwich UMI UMMISCO 209 (SU/IRD/UY1) "Programs must be written for people to read, and only incidentally for machines to execute."http://www.doesnotunderstand.org/

July 30, 2018

Re: [Pharo-users] transactions on pharo objects

by Esteban A. Maringolo

I think it is a tricky thing to do "in memory transactions", even without thinking about databases. You have to define what to keep and where to place the "original" values (inst. vars.) of the object. As a general purpose solution if you can do that, you end up implementing a mini gemstone in Pharo :) But what's sure is that you should have a mini object-table of the "touched" objects or do "explicit" registration of these objects like GLORP allows you to do. e.g. | p | p := Person new. System transaction: [:tx | tx register: p. p name: 'Nobody'. p age: 70. ]. self assert: p name equals: 'Nobody'. self assert: p age equals: 70. I'm using System here, to make it compatible with GemStone. #transaction: could be implemented in terms of #beginTransaction, #commitTransaction and internally use #abortTransaction if an unhandled Error is signalled. Regards! Esteban A. Maringolo El lun., 30 jul. 2018 a las 10:17, Peter UhnÃ¡k (<i.uhnak(a)gmail.com>) escribiÃ³: > > Hi, > > is there some library or approach how to do transactions in pharo? > And I don't mean database transactions, but directly in memory on Pharo objects... e.g. > > p := Person new. > > transaction do: [ > p name: 'Nobody'. > p age: 70. > ] on: Error do: [ > transaction rollback. > ]. > > self assert: p name equals: 'Nobody'. > self assert: p age equals: 70. > > transaction do: [ > p name: 'Somebody'. > p age: 1 / 0. > ] on: Error do: [ > transaction rollback. > ]. > > self assert: p name equals: 'Nobody'. > self assert: p age equals: 70. > > Any pointers appreciated. > > Thanks, > Peter

July 30, 2018

transactions on pharo objects

by Peter UhnÃ¡k

Hi, is there some library or approach how to do transactions in pharo? And I don't mean database transactions, but directly in memory on Pharo objects... e.g. p := Person new. transaction do: [ p name: 'Nobody'. p age: 70. ] on: Error do: [ transaction rollback. ]. self assert: p name equals: 'Nobody'. self assert: p age equals: 70. transaction do: [ p name: 'Somebody'. p age: 1 / 0. ] on: Error do: [ transaction rollback. ]. self assert: p name equals: 'Nobody'. self assert: p age equals: 70. Any pointers appreciated. Thanks, Peter

July 30, 2018

Re: [Pharo-users] a basic hash question

by James Foster

Werner, I would say that you are right, this is a problem. A (not un-common) source of subtle bugs in Smalltalk is missing this rule that equivalent objects must have the same hash. In GemStone the objects are not equivalent (Iâm not arguing that this is right, just that it avoids the problem you identify). I wonder what would happen if the hash comparison were added to the equivalence operator (#â=â)! James > On Jul 30, 2018, at 5:07 AM, werner kassens <wkassens(a)libello.com> wrote: > > Hi, > i guess i can subsume almost everything i know about hashes in one sentence: > it is my understanding that two objects that are equal (obj1=obj2. > -->true) have to have the same hash value (which is used for some > collection types), whereas objects where obj1=obj2 returns false should > have different hash values although it may happen that they have the > same one. > > now here things don't turn out exactly like that: > (1 to:4) = #(1 2 3 4). "true" > (1 to:4)hash = #(1 2 3 4)hash. "false" > well ok, actually these results make - pfffh, in a certain way - sense > to me, but i wonder what arguments the people in the know would use to > defend that result, if i would have another opinion? > werner > > >

July 30, 2018

Re: [Pharo-users] a basic hash question

by CÃ©drick BÃ©ler

But it raises the question if : (1 to:4)hash = #(1 2 3 4)hash should return true instead ?? Cedrick > Le 30 juil. 2018 Ã 14:51, CÃ©drick BÃ©ler <cdrick65(a)gmail.com> a Ã©crit : > > Just a quick guess seeing the implementation > > hash for collections is about hash of its elements > > SequencableCollection>>hasEqualElements: otherCollection > "Answer whether the receiver's size is the same as otherCollection's > size, and each of the receiver's elements equal the corresponding > element of otherCollection. > This should probably replace the current definition of #= ." > > | size | > (otherCollection isKindOf: SequenceableCollection) ifFalse: [^ false]. > (size := self size) = otherCollection size ifFalse: [^ false]. > 1 to: size do: > [:index | > (self at: index) = (otherCollection at: index) ifFalse: [^ false]]. > ^ true > > Cheers, > > CÃ©drick > >> Le 30 juil. 2018 Ã 14:07, werner kassens <wkassens(a)libello.com> a Ã©crit : >> >> Hi, >> i guess i can subsume almost everything i know about hashes in one sentence: >> it is my understanding that two objects that are equal (obj1=obj2. >> -->true) have to have the same hash value (which is used for some >> collection types), whereas objects where obj1=obj2 returns false should >> have different hash values although it may happen that they have the >> same one. >> >> now here things don't turn out exactly like that: >> (1 to:4) = #(1 2 3 4). "true" >> (1 to:4)hash = #(1 2 3 4)hash. "false" >> well ok, actually these results make - pfffh, in a certain way - sense >> to me, but i wonder what arguments the people in the know would use to >> defend that result, if i would have another opinion? >> werner >> >> >

July 30, 2018

Re: [Pharo-users] a basic hash question

by CÃ©drick BÃ©ler

Just a quick guess seeing the implementation hash for collections is about hash of its elements SequencableCollection>>hasEqualElements: otherCollection "Answer whether the receiver's size is the same as otherCollection's size, and each of the receiver's elements equal the corresponding element of otherCollection. This should probably replace the current definition of #= ." | size | (otherCollection isKindOf: SequenceableCollection) ifFalse: [^ false]. (size := self size) = otherCollection size ifFalse: [^ false]. 1 to: size do: [:index | (self at: index) = (otherCollection at: index) ifFalse: [^ false]]. ^ true Cheers, CÃ©drick > Le 30 juil. 2018 Ã 14:07, werner kassens <wkassens(a)libello.com> a Ã©crit : > > Hi, > i guess i can subsume almost everything i know about hashes in one sentence: > it is my understanding that two objects that are equal (obj1=obj2. > -->true) have to have the same hash value (which is used for some > collection types), whereas objects where obj1=obj2 returns false should > have different hash values although it may happen that they have the > same one. > > now here things don't turn out exactly like that: > (1 to:4) = #(1 2 3 4). "true" > (1 to:4)hash = #(1 2 3 4)hash. "false" > well ok, actually these results make - pfffh, in a certain way - sense > to me, but i wonder what arguments the people in the know would use to > defend that result, if i would have another opinion? > werner > >

July 30, 2018