Hi Max, On Oct 17, 2014, at 12:34 AM, Max Leske <[email protected]> wrote:
> >> On 17.10.2014, at 02:46, Ben Coman <[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? > 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. Eliot (phone)
