Liz Douglass

Book Club: Working Effectively With Legacy Code – Chapters 17, 18 and 19 (Michael Feathers)

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This week at book club we continued the three-chapter theme, taking on chapters 17, 18 and 19 of Working Effectively With Legacy Code. Chapter 17 is the most lengthy of the three and we spent almost all of our time discussing that one.

Chapter 17: My Application Has No Structure

In this chapter Feathers discusses why code bases degrade. He says that “They (applications) might have started out with a well-thought-out architecture, but over the years, under schedule pressure, they can get to the point where nobody really understands their complete structure.” He gives three possible reasons why a team may be unaware of this happening:

  • The system is so complex that it takes a long time to get the big picture
  • The system can be so complex that there is no big picture
  • The team is in a very reactive mode, dealing with emergency after emergency so much that they lose sight of the big picture

Feathers details some suggestions for how to communicate the intent of a system including ‘Telling the Story of the System’, a process where “One person starts off by asking the other ‘What is the architecture of the system?’ Then the other person tries to explain the architecture of the system using only a few concepts.” This is useful because “Often when we force ourselves to communicate a very simple view of the system, we can find new abstractions.”

  • I think all of us have used this technique when first coming to a project to try and get an understanding of the system. I usually have this type of conversation with each pair for the first couple of weeks on a project.
  • Ahrum said that in his experience developers find it very difficult to explain a system simply because we generally go into too much detail. Giving information about logging and security are examples including too much noise in the explanation.
  • Tom said that it’s important to speak with everyone on the project, not just the architect. He finds that architects generally focus too much on application layering.
  • I think this technique is related to Dan’s idea of having a project shaman.

Feathers also discussed Naked CRC. This is a lightweight version of CRC where there is no writing on the cards. “The person describing he system uses a set of blank index cards and lays them down on a table one by one. He or she can move the cards, point at them, or do whatever else is needed to convey the typical objects in the system and how they interact”. I’ve never used this approach before but Anita and I both said that we would like to try it because we think we’re visual learners. Tom suggested that combining the cards and a whiteboard could also be useful, especially to show interactions between components.

We also spent some time discussing other techniques for getting the big picture of an application, especially when encountering it for the first time:

  • Reading the code can be a good way to spot major concepts or the lack of them.
  • Raphael said that it’s useful to listen to the language that people use to describe the system and to compare that to the concepts in the code. Sarah and Mark both recently posted on this.
  • Tom said that he likes to make lots of mindmaps when he first goes onto a new project. He said he generally likes to observe for about a month before he attempts any large refactorings.
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Written by lizdouglass

December 19, 2009 at 7:28 am

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