> On 17.10.2014, at 02:46, Ben Coman <b...@openinworld.com> 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). 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 >> Sent from the Pharo Smalltalk Developers mailing list archive at Nabble.com.
