> On 17.10.2014, at 15:52, Nicolas Cellier <[email protected]> > wrote: > > > > 2014-10-17 15:49 GMT+02:00 Max Leske <[email protected] > <mailto:[email protected]>>: > >> On 17.10.2014, at 15:25, Eliot Miranda <[email protected] >> <mailto:[email protected]>> wrote: >> >> Hi Max, >> >> On Oct 17, 2014, at 12:34 AM, Max Leske <[email protected] >> <mailto:[email protected]>> wrote: >> >>> >>>> On 17.10.2014, at 02:46, Ben Coman <[email protected] >>>> <mailto:[email protected]>> wrote: >>>> >>>> Richard Sargent wrote: >>>>> Eliot Miranda-2 wrote >>>>>> On Wed, Oct 15, 2014 at 10:50 AM, Richard Sargent < >>>>>> richard.sargent@ >>>>>>> wrote: >>>>>>> One of the best things about Smalltalk is how easily we can say what we >>>>>>> mean. I think you would be better off creating a method named something >>>>>>> like >>>>>>> #hasSameEffectAs: to answer what you are presently using #= to do, and >>>>>>> change #= to answer the, in my opinion, more sensible "is the same as" >>>>>>> that >>>>>>> we conventionally think of #= meaning. >>>>>>> >>>>>> But that's the point. #= has to mean something and having it mean #== >>>>>> isn't useful, so one has to choose some value-based semantic for >>>>>> CompiledMethod>>#= and the one that's there is useful. Defining what #= >>>>>> means for some value type is far easier than defining what it might mean >>>>>> for something as complex as a CompiledMethod. The definition in >>>>>> Squeak/Pharo has been useful to me in implementing a closure-based >>>>>> system, >>>>>> so I'm unapologetic about the current definition. It is a good one but >>>>>> it >>>>>> doesn't preclude defining others. >>>>> An interesting response. You ignored the point that e.g. #hasSameEffectAs: >>>>> provides greater clarity and add an argument against something I didn't >>>>> say. >>>>> I also don't think defining equality for a CompiledMethod is particularly >>>>> difficult. If I were to recompile a method's source code, I would get a >>>>> new >>>>> instance of a CompiledMethod that would, in my opinion, be equal to the >>>>> one >>>>> already installed in the class (and perhaps cached in the VM's >>>>> optimizations). So one would be able to say that we would not replace an >>>>> existing CompiledMethod with an equal one. The current implementation of >>>>> #= >>>>> has no such characteristic, since it proclaims a CompiledMethod named #a >>>>> to >>>>> be equal to one named #z. >>>> >>>> @Richard >>>> >>>> That doesn't seem to be a good example for what your trying to say. >>>> Given... >>>> >>>> [1] SomeClass>>a "original instance" >>>> ^1 >>>> >>>> [2] SomeClass>>a "recompiled instance" >>>> ^1 >>>> >>>> [3] SomeClass>>z >>>> ^1 >>>> >>>> ...you seem to be saying that its useful to know if [1]=[2], >>>> but imply that is invalidated by [2]=[3] ? >>>> >>>> But [1]=[2] remains true, and just as useful for your example. >>>> >>>> >>>> @Max >>>> >>>> I guess to call it a bug, you bumped into a different use case >>>> where [2]=[3] is problematic. Can you describe that? >>> >>> Well, not problematic. Once you accept that neither selector nor class are >>> part of a CompiledMethod it is obvious that two instances with the same >>> byte codes produce the same hash. >>> >>> The actual problem is more one of understanding and use. The following code >>> answers a collection with the CompiledMethods Collection>>add:, >>> Collection>>do: and Collection>>remove:ifAbsent: >>> >>> Collection methods select: #isAbstract. >>> >>> All three CompiledMethods are implemented as ‘^ self >>> subclassResponsibility’, so they have the same byte codes. Now, if you take >>> that collection and make a set out of it you’ll lose Collection>>do: since >>> #do: and #add: produce the same hash, but #remove:ifAbsent: doesn’t because >>> the number of arguments is calculated into the hash (actually the >>> CompiledMethod header is). >> >> Surely the issue is that "aClass methods" should answer an IdentitySet right? > > Well, in the case of my example that wouldn’t change anything. As soon as you > put the methods into a set you’ll end up with less entries than before again. > Selectors are unique per class anyway so I don’t quite see the benefit of > using an IdentitySet over an OrderedCollection (or a Bag for that matter), > except for making it more obvious that the result of the message #methods > doesn’t need to be filtered further. > > I should add that the code, the student who discovered the clash wrote, > looked more like this: > > result := Set new. > Collection methods do: [ :m | > m isAbstract ifTrue: [ result add: m ] ]. > > Max > > > Why not just keep a dictionary, like methodDictionary select: #isAbstract or > something like that…
You’re right of course, there’s no need to put methods into a set. The code is from an exercise and the students aren’t used to Smalltalk, so they end up with all sorts of code. > >> >> >>> So, as long as you think of CompiledMethods as objects that have a name, it >>> looks like a bug and in my opinion this behaviour is something that messes >>> with the mind of newcomers. Just a (silly) idea: something like a >>> CompiledMethodWrapper might solve the problem (at least from the user >>> perspective; everything is slightly different from the VM perspective :) ), >>> as it could hold on to the class and the selector independently of the >>> actual CompiledMethod. >>> >>> In the end however, one doesn’t work with compiled methods a lot and the >>> hash situation is unlikely to cause a lot of problems (people working with >>> CompiledMethod usually know what they are doing). >>> >>> Cheers, >>> Max >>> >>>> >>>> >>>> cheers -ben >>>> >>>> >>>>> The blue book say #= means "Answer whether the receiver and the argument >>>>> represent the same component." The current implementation does so only for >>>>> some, in my opinion, counter-intuitive definition of "same component". >>>>> -- >>>>> View this message in context: >>>>> http://forum.world.st/CompiledMethod-hash-can-produce-clashes-tp4784722p4784779.html >>>>> >>>>> <http://forum.world.st/CompiledMethod-hash-can-produce-clashes-tp4784722p4784779.html> >>>>> Sent from the Pharo Smalltalk Developers mailing list archive at >>>>> Nabble.com <http://nabble.com/>. >> >> Eliot (phone)
