Chapter 17 Consistency

Consistency is a powerful tool for reducing the complexity of a system and making its behavior more obvious. If a system is consistent, it means that similar things are done in similar ways, and dissimilar things are done in different ways. Consistency creates cognitive leverage: once you have learned how something is done in one place, you can use that knowledge to immediately understand other places that use the same approach. If a system is not implemented in a consistent fashion, developers must learn about each situation separately. This will take more time.

Consistency reduces mistakes. If a system is not consistent, two situations may appear the same when in fact they are different. A developer may see a pattern that looks familiar and make incorrect assumptions based on previous encounters with that pattern. On the other hand, if the system is consistent, assumptions made based on familiar-looking situations will be safe. Consistency allows developers to work more quickly with fewer mistakes.

17.1 Examples of consistency

17.2 Ensuring consistency

17.3 Taking it too far

17.4 Conclusion

Consistency is another example of the investment mindset. It will take a bit of extra work to ensure consistency: work to decide on conventions, work to create automated checkers, work to look for similar situations to mimic in new code, and work in code reviews to educate the team. The return on this investment is that your code will be more obvious. Developers will be able to understand the code’s behavior more quickly and accurately, and this will allow them to work faster, with fewer bugs.