{PDF} Working Effectively with Legacy Code Michael Feathers

It should be no secret that the majority of commercial software development effort consists of dealing with other people’s poorly constructed code, yet this book is one of only a handful of sources that offer any practical advice for such undertakings, and the closest thing to a comprehensive reference on the subject so far as I know.

Here you’ll find dozens of useful techniques organized according to the kind of problem that they address, each explained concisely with concrete examples. Lots of them are things that I’ve had success with in the past, and of the ones I haven’t tried yet, there’s nothing in my 19 years of industry experience that leads me to doubt that they work.

A word of caution, though: It understates both the difficulty and the importance of having everyone who works on the same code to buy into the ideas it puts forth. Negligent programmers will resist change because they tend to benefit from “adverse selection” (look it up on Wikipedia), and you really don’t want to be the only one worrying about code coverage and maintainability while everyone else creates messes for you to clean up. Appealing to engineering wisdom and common interest is not always so easy as it sounds.

But on the whole, this is fine advice, and every programmer should own a copy. Not only will it help you to better the quality of your life by improving the state of your most troublesome projects, but also it will teach you to minimize the problems that you create in the first place, as well as how to fix those problems before they become too costly.