fogbugz entry for fixing the menu builder 13979 <https://pharo.fogbugz.com/default.asp?13979> PragmaMenuBuilder relies on modifying a collection while iterating over it.
2014-09-03 22:59 GMT+02:00 stepharo <[email protected]>: > Clement we should fix the code of the menu :) > > Stef > > > On 3/9/14 15:25, Clément Bera wrote: > > Hello, > > Sven you are right, the old compiler was consistent in the sense that it > always iterated over all the elements, including the ones added with #add: > and #addLast: while iterating over the collection. > On the other hand, VW is consistent with the Opal implementation for > #to:do: in the sense that they iterate only on the elements of the > collection excluding the ones added while iterating. > > #add:after: and co do not work well if you edit the collection while > iterating over it for sure :). > > It's too late for "don't modify a collection while iterating it" because > the system does it, for example, to build the world menu. So I think the > solution is in two steps: > - removing code which edit the collection while iterating over it. As most > frameworks work both on Pharo and VW and that the behavior is different I > think there shouldn't be that much, so fixing the Pharo image may be enough. > - be consistent in our collection protocol, basically by rewriting do: and > reverseDo: like that: > > FROM: > do: aBlock > "Override the superclass for performance reasons." > | index | > index := firstIndex. > [index <= lastIndex] > whileTrue: > [aBlock value: (array at: index). > index := index + 1] > TO: > do: aBlock > "Override the superclass for performance reasons." > firstIndex to: lastIndex do: [ :index | > aBlock value: (array at: index) ] > > > > > > 2014-09-03 14:05 GMT+02:00 Camille Teruel <[email protected]>: > >> >> On 3 sept. 2014, at 11:42, Clément Bera <[email protected]> wrote: >> >> > Hello guys, >> > >> > I was looking into the OrderedCollection protocols recently to see how >> well the sista optimizer perform with it methods, and I realized that this >> is completely broken. >> > >> > For example: >> > >> > col := #(1 2 3 4 5) asOrderedCollection. >> > col do: [ :elem | elem trace . >> > elem < 4 ifTrue: [ col add: col size + 1 ]]. >> > >> > => '12345678' >> > >> > However: >> > >> > col := #(1 2 3 4 5) asOrderedCollection. >> > col collect: [ :elem | elem trace . >> > elem < 4 ifTrue: [ col add: col size + 1 ]]. >> > >> > => '12345' >> > >> > This means that #do: and #reverseDo: iterate over all the elements of >> the collection,*including* the ones that you are adding while iterating >> over the collection, whereas all the other OrderedCollection protocols, >> such as #collect:, #select:, iterates over all the elements of the >> collection, *excluding* the ones you are adding while iterating over the >> collection. >> > >> > Marcus argued that one should not edit a collection while iterating >> over it, however this point is not valid as the World menu relies on this >> feature, using #do: to iterate over the elements of the OrderedCollection >> including the one it is adding while iterating over the collection. >> Changing the implementation makes the world menu display half of its items. >> > >> > I don't like this difference because it is inconsistent. For example, >> refactoring a #do: into a #collect: can simply not work because they do not >> iterate over the same elements if you are editing the collection while >> iterating over it. >> > >> > In VW, the protocols are consistent and iterating over a collection >> never iterates over the elements one is adding while iterating over it. >> Therefore, I believe most frameworks should expect this behavior (at least >> the ones cross smalltalk) which sounds the most correct. >> > >> > I think we should fix the world menu implementation and make the >> protocols consistent. Alternatively, we can let VW be a much more >> consistent Smalltalk environment than Pharo. What do you think ? >> >> >> The thing is to find alternative implementations that are efficient >> enough (no copy). Maybe we can get some inspirations from VW for that (how >> do they do BTW?). >> You should also check with other kinds of collection because they may act >> differently than OrderedCollection. >> So in the end it depends on the amount of effort needed to make all >> collections consistent with this new requirement and on the resulting >> overhead. >> If it's too much, I think that following the old advice "don't modify a >> collection while iterating it" is enough. If one really needs to do such >> kind of things he should consider an alternative design like using a zipper >> for example. >> >> Camille >> >> > >> > Clement >> > >> >> >> > >
