When to rewrite a code base from scratch

Question

I think back to Joel Spolsky\'s article about never rewriting code from scratch. To sum up his argument: The code doesn\'t get rusty, and while it may not look pretty afte

Answer 1

Start by writing a technical spec. If the code is that awful, then I bet there isn't a real spec either. So write a comprehensive and detailed spec - you need to write a spec anyway if you want to rewrite from scratch, so the time is a good investment. Be careful to include all details about the functionality. Since you are able to investigate the actual behavior of the app, this should be easy. Feel free to include improvement suggestions, but be sure to capture all details of the current behavior.

As part of the investigation you might consider writing some automated tests of to system to investigate and document expected behavior. Focus on black-box/integration testing rather than unit-testing (which the code will probably not allow anyway if it is that ugly).

When you have this spec you will likely discover that the app is actually much more complex than your first impression, and reconsider rewriting from scratch. If you decide to gradually refactor instead, the spec and tests will help you a lot. But if you still decide to go forward and rewrite, then you have a good spec to work from now, and a suite of integration tests which will telly you when your work is complete.