Table of content
- Abstract
- Which is the one weakness of OOP?
- How to overcome the one weakness of OOP? Solutions:
- 1. Professor Karl Lieberherr work on Adaptive programming and the Law of Demeter
- 2. Mock Objects and Growing object-oriented software, guided by tests
- 3. Less, The path to better design
- Comparing solutions
- References
Less, The path to better design
Sandi Metz in her speech 'Less, The path to better design' [2] takes on the challenge of the one weakness of OOP and presents design solutions that deal with changes in unstable object’s dependencies, both in the object structure and in the object graph.
The approach she presents is based on the idea that designers cannot predict the future but they can guard against it choosing carefully object dependencies, identifying those that are less stable and surrounded by more uncertainty and then aggressively decoupling them.
This approach is in tune with the second formulation of the The Law of Demeter that applies to the structure of the classes.
The solution that Sandi Metz presents, employs a design similar to the visitor pattern to decouple from unstable dependencies.
In the problem presented there are two objects that needs to interact to execute a task. The first object is known, under control and more stable, the second object is less stable because surrounded by more uncertainty. In order to reduce the coupling of the first one to the second, the second object acts like a Visitor in the Visitor pattern while the first object plays the role of the visited element. This design reverses the direction of the dependency, doing so it turns the unstable dependency relationship into a stable one.
Unlike the previous solution, this one does not make use of the Composite pattern to guard the code against changes in the object graph, because the language she uses is Ruby that supports duck typing, which serves the same purpose.
Here I name this solution as: “Visitor-like + Duck Typing”.