Design Patterns On Trial

Back in 1999, the OOPSLA conference held a show trial for the “Gang of Four”: Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides. Five years earlier, they had released their book “Design Patterns: Elements of Reusable Object-Oriented Software” at the very same conference, an act of subversion now seen as a crime against computer science. After hearing the case for the prosecution and for the defence, a simple minority of the conference delegates in attendance at the kangaroo court found the defendants guilty as charged.

The full indictment makes for some interesting reading, and it is clear that some real points are being made with tongues firmly in cheeks. “The Accused, by making it possible to design object-oriented programs in C++, have inhibited the rightful growth of competing object-oriented languages such as Smalltalk, CLOS, and Java.”

Perhaps this is a nod to Alan Kay’s OOPSLA 1997 outburst about not having C++ in mind when he invented the term Object-Oriented Programming. It’s certainly true that Smalltalk and CLOS are way less popular for Object-Oriented software implementation now than C++, but…Java? Really?

I could be asking “is Java really less popular than C++” here. But it’s also a good question to ask whether Java is really used to write Object-Oriented programs; the practice is so rare that Kevlin Henney recently had to do a talk reminding people that it’s possible.

The Accused, by distilling hard-won design expertise into patterns, have encouraged novices to act like experts.

In other words, they have advanced the field. By making it easier to today’s programmers to stand on the shoulders of those who came before, they have given them the skills previously afforded only by expertise. What a crime against computer science, making the field accessible!

Examples abound in history of people being tried for historical crimes when it’s important to make an example in current society. After the restoration of the monarchy in England and Scotland, Oliver Cromwell was exhumed and beheaded. Let’s rake the gang of four over the coals again. Here’s my addition to their indictment.

The Accused have, through their success in claiming the “Design Patterns” phrase as their own, maliciously tricked decades of programmers into believing that the whole idea behind Design Patterns is the catalogue of 23 patterns in their own book.

The point of design patterns is to have a patterns language, a shared glossary of solutions to common problems. When someone cites a pattern such as “microservice architecture” or “monorepo”, others know what they are doing, what problem they are solving, and the shape and trade-offs of their chosen solution.

But because people learn about “Design Patterns” from the GoF book (or, more likely, from Head First Design Patterns), they come to learn that Design Patterns are about Prototype, Flyweight, Iterator, and Template Method. They do not need these because their languages support them, therefore Design Patterns are old hat that nobody needs any more.

In fact they do not need those patterns because we stand on the shoulders of giants, and learned that these patterns were ubiquitously helpful in 1994. People are still publishing new design patterns (using the “particularly awkward and odious pattern format” of the Gang of Four), but these tend to be relegated to some dusty corner of academia. Worse, they tend to be written because nobody has written them yet (the “traditional standards of academic originality”), rather than because they represent “hard-won design expertise”.

In summary: design patterns are useful, because they let us quickly communicate a familiar solution with known properties when faced with a similar problem. The catalogue of design patterns in the book “Design Patterns” are useful, and because they have been useful since 1994 many of them have been subsumed into our tools at very basic levels. That book is a catalogue of useful design patterns from 1994, it is not all there is to know about design patterns.

Design patterns are dead. Long live design patterns!

About Graham

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One Response to Design Patterns On Trial

  1. Pingback: Aphorism Considered Harmful | Structure and Interpretation of Computer Programmers

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