Niko Schwarz <niko.schwarz at gmx.net> wrote:
	Is there a way to index OrderedCollections beginning at 0?
	
I can think of several approaches, starting with defining your own
version of OrderedCollection.

While I personally like to start indices at 0, since every existing
"array-like" collection in Smalltalk starts at 1, I think it would
be unwise to introduce something different.  I am a bear of very
little brain.  I can handle rules like "In C, arrays start at 0.
In Smalltalk, arrays start at 1.  In the Algols, each array starts
wherever you want."  I have real trouble with rules like "in this
copy of Squeak, most collections start at 1, except for a few that
don't."

    Collection subclass: #OriginShiftedSequence
        instanceVariables: 'sequence delta'
        &c &c

    at: index
        ^sequence at: index + delta
        
    at: index put: element
        ^sequence at: index + delta put: element
        
    includesKey: index
        ^index + delta between: 1 and: sequence size

    origin
	^1 - delta

    origin:
	delta := 1 - origin

    on: aCollection
	self assert: [aCollection isSequenceable].
	sequence := aCollection

    do: aBlock
	sequence do: aBlock

    "class methods"

    on: aCollection origin: origin
        ^self new on: aCollection; origin: origin; yourself

Now you can do
    os0 := OriginShiftedSequence on: anOrderedCollection origin: 0.

If you go this route, you will have to write a lot of "forwarding"
methods.  You might like to base it on my EnumerationAdapter class,
which will define many of those methods for you.