What is a good maintainability index using Visual Studio 2008 code analysis?

Question

My company recently purchased TFS and I have started looking into the code analysis tools to help drive up code quality and noticed a good looking metric "maintainability index". Is anyone using this metric for code reviews/checkins/etc? If so, what is an acceptable index for developers to work toward?

Answer 1

The maintainability index is not as much a fixed value you look at, it's more of an indication that code is hard to understand, test and/or debug. I usually try to keep high-level code (basically anything except for the real plumbing code) above 80, where 90+ would be good. It adds a competitive element to programming as maintainable as possible to me.

The code analysis tool really shines in the area of dependencies and the number of branches within a method though. More branches mean harder testing, which makes it more error-prone. Dependencies, same thing.

In other people's code, I use the maintainability index to spot possible bad parts in the code, so I know where to review it. Also, methods/classes with a high number of lines are an indication of poor code to me (unless it can't be avoided, again, the plumbing works).

In the end, I think it mainly depends on how often your code will change. Code that's expected to change a lot has to score higher in maintainability than your typical 'write once' code.