uniqueInstance on Seaside Smalltalk

I'm trying to implement the Singleton pattern on Seaside. Here is my code:

        uniqueInstance
            uniqueInstance ifNil: [ uniqueInstance := self createInstance].
            ^ uniqueInstance

    createInstance
        ^ self basicNew

initialize
    users:= OrderedCollection new.

On the instance side I have users that is the instance variable. When I call Application uniqueInstance initialize works. When I inspect the users variable, it said "Identity Set" instead of an OrderedCollection.

Can anybody give me a solution to my mistake?

Based on a (Pharo) mailing list discussion regarding singletons I wrote about some variations some time ago https://www.peteruhnak.com/blog/2015/12/06/singleton-variations/ .

But the gist of the singleton is:

1. (usually) block MyThing class>>new
   • because it is a singleton
2. call super new or self basicNew initialize when creating the instance
   • this is to go around the blocked new; if your dialect doesn't call initialize automatically then use the latter form
3. (optionally) add MyThing class>>reset to nil the instance
   • for convenience mostly (with <script: 'self reset'> pragma can be made even better)

So in your case it can be something like this:

Users class>>uniqueInstance
    ^ uniqueInstance ifNil: [ uniqueInstance := super new ]

Users class>>new
    self error: 'Users is a singleton -- send uniqueInstance instead'

Users>>initialize
    users:= OrderedCollection new

And if you are in Pharo, feel free the explore the existing implementations

MessageBrowser browse: (#uniqueInstance implementors select: #isMetaSide).
MessageBrowser browse: (#default implementors select: #isMetaSide).
MessageBrowser browse: (#current implementors select: #isMetaSide).