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Essential Skills for the Agile Developer: Avoid Over- and Under-Design

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How do you avoid over- or under-designing your code? As Ward Cunningham once said, "Take as much time as you need to make your code quality as high as it can be, but don't spend a second adding functionality that you don't need now!" This chapter covers this "mantra for development: write high-quality code, but don't write extra code.
This chapter is from the book

Developers tend to take one of two approaches to programming. Many think they need to plan ahead to ensure that their system can handle new requirements that come their way. Unfortunately, this planning ahead often involves adding code to handle situations that never come up. The end result is code that is more complex than it needs to be and therefore harder to change—the exact situation they were trying to avoid. The alternative, of course, seems equally bad. That is, they just jump in, code with no forethought, and hope for the best. But this hacking also typically results in code that is hard to modify. What are we supposed to do that doesn't cause extra complexity but leaves our code easy to change? The middle ground can be summed up by something Ward Cunningham said at a user group: "Take as much time as you need to make your code quality as high as it can be, but don't spend a second adding functionality that you don't need now!" In other words, write high-quality code, but don't write extra code.

This chapter is admittedly more of a new mantra than it is a detailed description of a technique to implement. This chapter takes advantage of what we learned in Chapter 5, Encapsulate That!, and sets the groundwork for Chapter 11, Refactor to the Open-Closed.

A Mantra for Development

We believe developers should have a particular attitude when writing code. There are actually several we've come up with over time—all being somewhat consistent with each other but saying things a different way. The following are the ones we've held to date:

  • Avoid over- and under-design.
  • Minimize complexity and rework.
  • Never make your code worse (the Hippocratic Oath of coding).
  • Only degrade your code intentionally.
  • Keep your code easy to change, robust, and safe to change.

Before we can discuss these mantras, we need to be clear what we mean by quality code. Appendix B, Code Qualities, provides a thorough explanation of the specific qualities referred to in this chapter. We'll give a brief summary of code quality here, but interested readers may want to read the more extensive narrative in the appendix.

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