Andres,

I think your implementation of

!SequenceableCollection methodsFor: 'copying' stamp: 'SqR!!!! 4/10/2000
09:20'!
forceTo: length paddingWith: elem
        "Force the length of the collection to length, padding 
        if necessary with elem. Note that this makes a copy.

        Much much faster, SqR!! 4/10/2000 09:19"

        | newCollection copyLen padded toPad thisPad |

        newCollection _ self species new: length.
        copyLen _ self size min: length.

        "Copy bulk"
        newCollection replaceFrom: 1 to: copyLen
                with: self startingAt: 1.

        "Fast out"
        copyLen = length ifTrue: [^newCollection].

        "Fill at the end. Tres cool method"
        newCollection at: copyLen + 1 put: elem.
        toPad _ length - copyLen. padded _ 1.
        [padded = toPad] whileFalse:
                [
                        thisPad _ padded min: toPad - padded.
                        newCollection 
                                replaceFrom: copyLen + padded + 1 to:
copyLen + padded + thisPad
                                with: newCollection startingAt: copyLen
+ 1.
                        padded _ padded + thisPad.
                ].
        ^newCollection! !

is fast (assumed it works), because >>replaceFrom:to:startingAt: is
realized by calling primitive: 105 for many subclasses. But it is
complicated.

I think it would be better to create a new method like 

SequenceableCollection>>
from: start to: stop put: anElem
	"Replaces elements from start to stop by anElem for all valid indices."
	start to: (stop min: self size) do: [:ix | self at: ix put: anElem].
	^self

, which *could* be implemented as a primitive for the subclasses with
fast >>replace:... primitive,
and then change >>forceTo:paddingWith: to

SequenceableCollection>>
forceTo: length paddingWith: elem
	"Force the length of the collection to length, padding if necissary
	with elem.  Note that this makes a copy."
	| newCollection copyLen |
	newCollection _ self species new: length.

	length > self size ifTrue: [self from: size + 1 to: length put:
anElem].

        copyLen _ self size min: length.

        "Copy bulk"
        newCollection replaceFrom: 1 to: copyLen
                with: self startingAt: 1.

	^ newCollection
.

Note: I haven't compiled this code.

Regards,

Stephan

P.S.: Your Squeak (2.6) is not very up to date...
-- 
Stephan Rudlof (sr at evolgo.de)
   "Genius doesn't work on an assembly line basis.
    You can't simply say, 'Today I will be brilliant.'"
    -- Kirk, "The Ultimate Computer", stardate 4731.3