On Nov 5, 2007, at 6:39 PM, Rob Withers wrote:

> What gaurantees that doing loops with #nextObject won't cause  
> cyclic looping whereby you process the same set of objects over and  
> over again?
>
> The work I was doing was testing changing the parser to eliminate  
> #ifTrue: macros from compiled methods and recompiled the entire  
> image.  I saved the image.  When I started the image it was  
> frozen.  I broke into it and it was looping in the method  
> CommandHistory class>>#forgetAllGrabCommandsFrom:.  I took the loop  
> and modified it slightly to see what it was processing:
>
>    | object count objects |
>    objects := OrderedCollection new: 1000000.
>    count := 0.
>    object _ nil.
>    [0 == object or: [count > 500000]] whileFalse: [
>        count := count + 1.
>        objects add: object.
>        object isMorph ifTrue: [object removeProperty:  
> #undoGrabCommand].
>        object _ object nextObject].
>    objects


I think your test is wrong 0 == object while always evaluate to false.
#nextObject return the nextObject in memory. But integer are not  
object in memory they are pointer (need to be confirm).


So you could try:

| object count objects |
    objects := OrderedCollection new: 1000000.
    count := 0.
    object := nil.
    firstObject := object
    [firstObject == object or: [count > 500000]] whileFalse: [
        count := count + 1.
        objects add: object.
        object isMorph ifTrue: [object removeProperty:  
#undoGrabCommand].
        object _ object nextObject].
    objects

HTH

	Mth

>
> It was looping through objects defined by this loop, block contexts  
> defined by my change to #ifTrue: bytecodes - they now create block  
> contexts.
>
> [] in UndefinedObject>>DoIt {[object removeProperty:  
> #undoGrabCommand]}
> [] in UndefinedObject>>DoIt {[count > 500000]}
> OrderedCollection>>add:
> OrderedCollection>>addLast:
> [] in OrderedCollection>>addLast: {[self makeRoomAtLast]}
> False>>or:
> [] in UndefinedObject>>DoIt {[object removeProperty:  
> #undoGrabCommand]}
> [] in UndefinedObject>>DoIt {[count > 500000]}
> . . .
>
> What guarantee is there supposed to be that #nextObject won't loop  
> back into a cycle?  What did I do to break that guarantee and how  
> can I reestablish it?
>
> cheers,
> Rob
>