[Cuis] PluggableListMorph

[Dan Norton]

Hello All,

Please review the following for accuracy. It's not complete. It's a start on a "Principles of 
Operation" for applying PluggableListMorph for fun and profit. Maybe it should be called 
"PluggableListMorph for Dummies". I'm especially interested in whether you agree with the 
"coincidental" statement.

PluggableListMorph is designed to work as part of one or more views on a model in the MVC 
paradigm (Note 1). The model is not directly aware of the existence of any view; instead, it 
signals changes in itself by broadcasting symbols with the #changed: method. In this way, 
any view which is related to the model can detect the changes by examining the symbol in its 
#update: method. Thus while the model is not explicitly aware of a view, there is an implicit 
relationship in that a view must know the significance of the symbols broadcast by the model 
in order to respond appropriately. Views are dependents of a model and therefore the model 
is a sponsor of views. Use of the #changed: and #update: methods is the essence of the 
Smalltalk dependency mechanism (Inside II).

The model sends #changed: and as a result, all dependents (e.g. views) on it receive 
#update:. In the #update: method, the view examines the symbol and decides what, if 
anything, to do. While the symbol  is, in practice, often identical to the name of a method, this 
is coincidental and unfortunately a source of confusion and misdirection.

Note 1. The MVC paradigm is mentioned here for historical context. PluggableListMorph can 
also be employed in other design schemes.

Inside II. LaLonde and Pugh, "Inside Smalltalk, Volume II"

Thanks,
 - Dan