Add, Don't Modify Pattern

30 Août 2008
Posted in Artikelen - Computers

Intent

We want to be able to grow our domain models. They must be infinitely scalable. Growing an already large model should not be more difficult than a small model. Change comes in two forms: changing existing functionality, or adding new. There should be as little difference between the two, regarding testing, validating, and modelling.

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Problem

Solution

Don't change existing objects, not for changing existing functionality, nor to add new functionality. Existing test cases should not need to be modified. Functionality is modified by adding more objects. Since the model has been created using the Active/Passive pattern it is a loosely coupled model that does not hinder us in doing this.

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Comments (1)

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Hi Rob, a question regarding this.
Let's say we want to add functionality to our object. When applying this pattern, it means more objects through inheritance. But that would mean strong coupling (I don't want to use inheritance n concrete objects).
Do you know how to deal with this?

Eddy , 16 mai 2010

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