Thinking about Design Patterns

I have this friend who is an ambitious young corporate climber. When I was started out as a team lead, I was totally overwhelmed by the office politics I was suddenly exposed to. Naturally, I turned to my friend for advice. She told me to read Machiaveli’s “The Prince”. So I did. Its an interesting read, but not that amazing as far as management advice goes. When I later tried to discuss the book with my friend, I found out that she never actually read the book herself – she just thought it is good advice.

6 years later and I still believe people when they tell me that I have to read a book. I’m naive like that.

So I spent the last two weeks reading “The Timeless Way of Building”. Its an architecture book. Architecture as in cities and buildings. The reason I spent two weeks reading a professional book intended for a different profession is that at some point in history (1994, I believe), some people though that the ideas in the book are relevant to software development. These days you can’t really be a Java developer without being fully fluent in the development pattern language.

And of course, everyone was saying “You have to read The Timeless Way of Building. It will change the way you think about software.”. From my days in development, I still remember quite a bit of stuff about design patterns, and I never really liked that particular approach to software development, but I didn’t really figure out why. After reading the authoritative source on patterns, I can say the following:

  1. Christopher Alexander had some good ideas about patterns. The book is readable to non-architects and is very enlightening. I recommend reading it if you are interested in what makes some cities and buildings feel better than others.
  2. I am pretty sure that his advice on how to design good buildings is not really applicable to software development field.
    A lot of his ideas are based on the fact (which he did the research to prove) that people intuitively know how buildings should be designed, and that when you ask a large number of people “How do you imagine you will feel in such room?”, you’ll get an overwhelming consensus. This is far from being true in the software field.
  3. What is common known today as software design patterns is so far removed from what Christopher Alexander recommended for architects, that software developers should really go and find a different name for what they are doing.

I’m still rather shocked by the differences between Christopher Alexander’s patterns, and what design patterns look like today. It is not few tiny differences that occur whenever ideas are translated from one domain to another. Some of the changes are profound.

First of all, Christopher Alexander says that patterns describe the way people already do things. “Night Life” and “Parallel Streets” existed before the book “A Pattern Language” was written. I’m not at all sure this is the case for design patterns. People buy design pattern books to learn the patterns themselves, not just the language or which patterns are better than others.

Second, patterns should have an intuitive meaning and intuitive name. Again, you don’t need a book to know what is a “Bus Stop” or “Small Parking Lots”. You may want to read the book to find out why they are a good idea, or how to make a good bus stop, but you know what it is. I don’t believe that anyone knew what is an “Abstract Factory” before reading a document about design patterns. Even patterns that have been used for decades got a fancy name. It can take a while to figure out that a Singleton is a global variable. One of the simplest and most common patterns in software development “A function that does exactly one task” is missing from software design patterns. “A Loop” is also a pattern which is missing in action. All this gives the wrong impression that patterns are very complicated and something that can be mastered by experts only – which is exactly the opposite of what Christopher Alexander intended.

Third, patterns are abstract concepts. They are always implemented in a different way, because the entire idea is to be sensitive to the context, which is never the same twice. There is a pattern called “Six-foot balcony”, but it would be wrong to mass-manufacture six-foot balconies and start attaching them to buildings. Six-foot balcony is the idea, the exact shape of the balcony will be designed to match the building, the view, the trees, the sun, etc.
So it is rather annoying to discover that all patterns have “implementation examples”, which developers enjoy copying into their code. I’m all for code reuse, but this is not patterns mean.Wikipedia has a decent description of what defines a pattern, and “being implementable in one or two simple classes that can be copy-pasted” is not part of it.

Executive summary: “Timeless Way of Building” is an interesting book on architecture, with some good insights about how humans like to live and a bit of a Zen feel. You will not learn anything about software development from reading it. If you already know software design patterns, you will be struck by how different the ideas in the book seem.

One Comment on “Thinking about Design Patterns”

  1. Couldn’t agree more. Personally I find patterns a good basis for reasoning about potential solutions to a problem. But nowadays many people are probably so busy and have narrow timelines that they only look for example code to copy. The bad thing is: if I can copy it and reuse it, it should not be in a book but rather in a library I can buy or download. Patterns on the other hand help you reason about code entities (e.g. classes, objects). their responsibilities and how they interact. (CRC cards are also a good simple tool for this.) Separation of concern is a very important concept because it determines whether code is reusable or not.

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