Archive for the 'Quotes' Category

I recently commented on a provocative post by Jovan Sranojlovic called “Do Not Use Design Patterns Upfront” He made some thoughtful observations on why design patterns are important to software engineering and how they can a abused in that context as well. However, I disagreed with his basic thesis that design pattern should only be applied in a code refactoring context and not before. Based on his argument, thinking in design patterns upfront, based on the intent and purpose of code in not good, and even harmful. I tweeted my disagreement with a link to JUnit A Cook’s Tour, an example of, what I thought was, thinking in design patterns at the application design stage. The resulting tweet stream follows:

“Do Not Use Design Patterns Upfront” http://tr.im/uI3a – I don’t agree. Beck & Gamma did just that with JUnit http://tr.im/uI3z #asdp
1:09 AM Jul 30th by @chandimac

@chandimac no we didn’t. we explained junit with patterns, but we started with one tiny test and grew the whole thing from there.
6:33 AM Jul 30th by @kentbeck in reply to @chandimac

@kentbeck TX for the clarification. Do you recommend “thinking in patterns” early or should they be added at a later refactoring stage?
6:30 AM Jul 31st by @chandimac in reply to @kentbeck

@chandimac i prefer to put patterns in place just before they become useful. if i can’t see how to do that, then soon after.
6:51 AM Jul 31st by @kentbeck in reply to @chandimac

JUnit A Cook’s Tour explains the design of a system by starting with nothing and applying patterns, one after another, until you have the architecture of the system. As Kent pointed out, the article was written that way, and I had incorrectly assumed that JUnit was developed that way as well.

Design Pattern wisdom in 140 characters

I put patterns in place just before they become useful. If I can’t see how to do that, then soon after.

– Kent Beck

I was quite intrigued by Kent’s reply to my follow up question. It got me thinking about a bunch of issues. What does it mean for a design pattern to be “useful?” How much before is “just before?” What does it mean to “put patterns in place?”

I was so intrigued that I re-read a bunch of stuff on refactoring and design patterns by Beck, Gamma, Kerievsky and Alexander. I try my best to answer some of the questions raised in the remainder of this post – or more appropriately, reconcile some of my cognitive dissonance. Continue reading ‘Integrating design patterns “just before they become useful”’