Sunday, August 12, 2012

Refactor at Your Own Risk

Often when we're left to work in someone else's code, we think it's poorly written and seek to improve it or, perhaps worse, rewrite it entirely. Refactor at your own risk, however. Doing so often has unintended consequences or provides little value. Here are my general guidelines:

  • Don't refactor code that won't change

When reworking code, you get the biggest bang for your buck with the code that your programmers work in nearly every day. You know, those places in code that are constantly changing when bugs are discovered or requirements change.

Now contrast this with refactoring that class that hasn't changed in years. Generally we refactor a piece of code so that it will be easier to make changes in the future. If a class is fairly static*, then refactoring provides little to no benefit and only increases the risk of adding new bugs.

  • Refactor in increments

Refactoring works best when done in small increments. Joel Spolsky reminds us to avoid the big rewrite:
We're programmers. Programmers are, in their hearts, architects, and the first thing they want to do when they get to a site is to bulldoze the place flat and build something grand. We're not excited by incremental renovation: tinkering, improving, planting flower beds.
There's a subtle reason that programmers always want to throw away the code and start over. The reason is that they think the old code is a mess. And here is the interesting observation: they are probably wrong. The reason that they think the old code is a mess is because of a cardinal, fundamental law of programming:
It’s harder to read code than to write it.

  • Be wary of refactoring uncovered code

Refactoring is best done when there is a suite of unit tests that assert the correct behavior of the class. In the absence of tests, consider first writing some tests or perhaps avoid refactoring altogether.

  • Use refactoring tools

Where possible, use tools that will perform a variety of common refactors, such as renaming variables, extracting methods, and changing method signatures.

Don't rework code for no reason. Make those changes that will increase the readability and maintainability of your code. As always, the benefits must be weighed against the risks. Remember that, to your users, a working product is king.

*no pun intended

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