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