The VisualWorks GUI builder generally installs value holders in
instance variables of the application model. The value-holder
installation is done by an application-model getter that creates a value
holder the first time that it is called. The getter exhibits the following
general pattern, in which the selector and instance variable have the
same name:
selector
^ instance variable isNil
ifTrue: [instance variable := initial value asValue]
ifFalse: [instance variable]