At the SoCraTes 2011 conference I facilitated a session about applying the S.O.L.I.D. design principles to dynamic OO languages and to functional languages.
I prepared some Flipcharts with the SOLID principles (Slideshare), code examples for Java, Ruby, Scala and Clojure (GitHub) and a paper with a description of the SOLID design principles and some thesis about their application to dynamic OO and functional languages (PDF).
I am not sure if the session can be counted as a success. We had three groups. One was working on the application of SOLID to dynamic OO languages with the Ruby code examples. The second group was working on the application of SOLID to statically typed functional languages with the Scala code examples. The third group worked on the application of the SOLID principles to dynamic functional languages with the Clojure examples.
The results were ambiguous and we didn’t find final answers. What became clear is that the SOLID design principles can be applied to all these types of languages. What stayed fuzzy was the question if that application would be useful for the everyday work with these languages. While I tend to think that in fact not every principle is useful in every languages there were others having the opposite opinion.
One of the problems within the workshop was that today OO thinking is baked into out heads. And so the Scala and the Clojure group created designs in OO style. And if you do that with a functional language of course SOLID is applicable and at least to a certain degree useful 🙂
In the end of the session we had a discussion in a smaller group of people if it may be to misleading to apply SOLID to functional programming. Perhaps it drives our thinking in the wrong direction. Perhaps it would be better to go back to the underlying principles of cohesion and coupling and creating new design principles for functional languages on top of these. And perhaps such design principles already exist and I am just to blind to see them.
So: There is still a lot to learn and a lot of experiments to do. If you like to contribute I would really much appreciate it.