Monday, November 30, 2009

Design Patterns 15 years later

Design Patterns 15 Years Later: An Interview with Erich Gamma, Richard Helm, and Ralph Johnson was recently featured on Lambda the Ultimate.

Some say design patterns are just work-arounds for the defects of C++. The paper Essential Programming Paradigm argues that design patterns occur because the programming paradigm disallows certain run-time composition of dynamic and static code. The GoF authors confirm that their design patterns fit object-oriented languages, and arise specifically from experience with C++ and Smalltalk, so are tied to language of implementation. "Design patterns eventually emerge for any language. Design déjà-vu is language neutral." Different design patterns may be emerging for dynamic languages or for functional languages.

They discuss the development of more design patterns beyond the 23 examples chosen for the Design Patterns book. Eric Gamma suggest some sort of collective intelligence approach for editing design patterns and rating their importance and applicability. Sounds like a good idea. Some new patterns they mention as candidates for inclusion in a revised set are: Null Object, Type Object, Dependency Injection, and Extension Object/Interface. Their new (draft) categorization of design patterns looks like this:

They seem to have dropped several, some of which I won't miss. but why axe composite or observer? And bridge, maybe not the most useful in practise, but when I finally understood what they meant, I felt like I had accomplished something.

Design patterns links