On Fri, Mar 1, 2019 at 12:02 PM Sven Van Caekenberghe <s...@stfx.eu> wrote:
> Ah, it is an optimisation: if the first #== fails, but the argument is > also a Symbol, then that means the are different for sure, so false is > returned early, instead of failing in super's #= after that. > > And with ByteSymbol and WideSymbol, although they are exclusive (can never > be equal), they can be different and if they are both Symbols, then you can > return early (not just when their classes differ). > Thanks for explaining that! As an aside, this is the kind of information that should be in a method's comment. Rationale and explanation, rather than what it does. > > On 1 Mar 2019, at 18:40, Sven Van Caekenberghe <s...@stfx.eu> wrote: > > > > Why ? Please explain ... > > > >> On 1 Mar 2019, at 18:02, David T. Lewis <le...@mail.msen.com> wrote: > >> > >> On Fri, Mar 01, 2019 at 05:18:27PM +0100, Sven Van Caekenberghe wrote: > >>> > >>> > >>>> On 1 Mar 2019, at 17:08, Petr Fischer via Pharo-users < > pharo-users@lists.pharo.org> wrote: > >>>> > >>>> > >>>> From: Petr Fischer <petr.fisc...@me.com> > >>>> Subject: Symbol equality method #= - weird condition in the Pharo > sourcecode > >>>> Date: 1 March 2019 at 17:08:03 GMT+1 > >>>> To: pharo-users@lists.pharo.org > >>>> > >>>> > >>>> Hello, this is Symbol equality method in Pharo: > >>>> > >>>> 1: = aSymbol > >>>> 2: "Compare the receiver and aSymbol." > >>>> 3: self == aSymbol ifTrue: [^ true]. > >>>> 4: self class == aSymbol class ifTrue: [^ false]. > >>>> 5: "Use String comparison otherwise" > >>>> 6: ^ super = aSymbol > >>>> > >>>> Look at line 4 - what does it mean? That's wrong, isn't it? > >>>> > >>>> Typically, every symbol comparisons end up in line 3, but if you do > some work with forward proxies for example, condition on line 3 is "false" > and then weird things on line 4 happens. > >>>> > >>>> If line 4 and further are correct, can someone explain a little? > >>>> > >>>> Thanks! pf > >>> > >>> Yes, that looks weird. Line 4 should probably be removed, unless I am > missing something. > >> > >> It is wrong in a Spur image, because we now have subclasses of Symbol. > >> But removing line 4 is not the right solution. See Nicolas' > implementation > >> in Squeak: > >> > >> Symbol>>= aSymbol > >> "Compare the receiver and aSymbol." > >> self == aSymbol ifTrue: [^ true]. > >> aSymbol isSymbol ifTrue: [^ false]. > >> "Use String comparison otherwise" > >> ^ super = aSymbol > >> > >> Dave > >> > >>> > >>> Symbols are by definition always #== so in that sense, #= should not > even be implemented (as #= on Object is defined as #==), but since its > direct super class String already overwrote #=, it has to follow. > >>> > >>> The super call in line 6 is what allows Symbols and String to be > compared. > >>> > >>> I would say line 4 is a kind of sanity check, but probably not needed. > > > > >
