Nmingott: imported material

2025-05-12T20:42:13Z

imported material

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* In '''Cuis-6''' there isn't anymore a '''Model''', there instead an '''ActiveModel''' class, but the name 'model' a very frequent in the code. You can still find '''Model''' in '''Squeak-5.3''' and '''VisualWorks-8.3''' if you wish to check out some implementation.
* We have seen (here) how to manage Dependency with the Parent / Dependent strategy. But where do all the relations involving objects are stored ?
* There relations are stored by default in the class variable '''DependentsFields''' of the class '''Object''' which is a specialized dictionary, where at every key corresponds an object who is Parent and its values are a list of Dependents objects.
* You can well understand that if there are a lot of dependencies the dictionary in DependentsFields becomes very large and also, there is another problem. If a dependent lost all references in the VM except for a forgotten relationship link in DependentsFields it will stay there and will not be garbage collected.
* To avoid these two problems, and for performance reasons, it was introduced the class '''Model''' which is a subclass of '''Object''' and a has an instance variable field called <code>dependents</code> where all the dependents are stored.
* In this way, if '''objA''' is a intended to be a Parent and you make it as a '''Model''' subclass instance, all its depency relationships will be localized into '''objA''' itself avoiding a large centralized permanent dictionary and also, once you delete '''objA''', you are sure all its dependents will be free to be garbage collected, when necessary.

The Dependency Mechanism - part 2 - Revision history

Nmingott: imported material