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.
>
>
