[Vm-dev] Re: [squeak-dev] Re: Separate TeaTime (was Re: Re: Teleplace is hiring...)

[Andreas Raab]

On 3/30/2011 4:12, Eliot Miranda wrote:
> Classes *don't* inherit from nil.  nil is at the end of their 
> superclass chain.  That's different from inheriting.
>
> At least in current images UndefinedObject includesBehavior: nil is 
> false, which seems right to me.  nil is not a behavior; its use as the 
> sentinel at the end of the superclass chain doesn't imply it is a 
> behavior.  So I propose that we change includesBehavior:ThatOf: to 
> something like
>
> StackInterpreter methods for plugin primitive support
> includesBehavior: aClass ThatOf: aSuperclass
> "Return the equivalent of
> aClass includesBehavior: aSuperclass.
> Note: written for efficiency and better inlining (only 1 temp)"
> | theClass |
> <inline: true>
> aSuperclass = objectMemory nilObject ifTrue:
> [^false].
> theClass := aClass.
> [theClass = aSuperclass ifTrue:
> [^true].
> theClass ~= objectMemory nilObject] whileTrue:
> [theClass := self superclassOf: theClass].
> ^false
>
> I don't think this will affect anything other than FFI and Alien since 
> those are the only uses I can find, and in my reading of that code the 
> proposed change seems fine; safer in fact.
>
> Agreed?

Sounds reasonable to me. The one thing to check is if there are any 
places that currently assume that includesBehavior:ThatOf: returns true 
for a nil argument. If so, we can still add an explicit check that tests 
for interpreterProxy classAlien to be nil but I agree that the above 
would be the better solution.

Cheers,
   - Andreas

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