Slashdot Mirror

Hmmm... reminded me of an article about code rewriting that slashdot posted a while back.

Slashdot Story: How To Make Software Projects Fail

Relevant interview link

Refactoring is not re-writing. Refactoring is a methodical approach to moving, redesigning, and making the code cleaner. It's not throwing away and starting from scratch. The two words are wholly semantically different.

In his book, Refactoring, Martin Fowler talks about how code "smells". He identifies a whole slew of reasons why code can "smell" bad, such as having a method that's too long, having a method on the wrong object, incorrect use of polymorphism, etc. He then outlines "Refactoring Patterns" which can be applied to certain "smells" to make the code more managable.

The last project I managed was a 3 month re-write of over 75,000 lines of code for an auction component that had gotten way out of control. The original component integrated with a very very poorly written (yet still very expensive) auction engine, and our task was to take it out.

Because there was no time allotted to proper requirements gathering, the powers that be decided that we could use the existing system as a requirements base, and just make the new system "act" like the old one.

So I was thrown two things: A staff that was inexperienced in design, and a lack of requirements. We were re-writing from scratch -- throwing all of the code away and starting again. I'm one of the only ones on my team that actually knows what refactoring means, let alone how to apply it.

So we built the new system based on a solid design. We even did the design in UML. But that only goes so far. Given a properly designed system, there is still another lower step -- how to actually implement the code. Invariably, the design doesn't take into account helper methods that are necessary, other objects, etc. Because we were on a tight schedule, I left it up to each developer to design these new tidbits.

If they had known what they were doing, everything would have been fine, but there are several places where the code is absolutely abysmal. It's not that it will perform poorly or is totally unmanagable, but in some places it's close.

Granted, the business rules for the system are some of the most complex I've ever seen, but if the developers had known more about refactoring, they might have made better choices.

There's a whole notion of Quality here that should be discussed as well. Most good has a good enough quality, and though it looks ugly, I'd throw it away. There's an interesting interview by Joel (a former microsoft programmer) which tackles these problems of Quality head on. I also reccommend reading Zen and the Art of Motorcycle Maintenence: An Inqiry into Values for a pretty good discussion of the whole notion of quality.

I'd say just keep the codebase unless you are totally switching languages (or in our case taking out a 3rd party integration). Otherwise if you re-write you'll wish you hadn't. The new codebase will end up being in the same state as the old codebase, it'll just take a little bit more time to get there.

I'd also reccommend just doing a performance test of the site, and find out which modules really need to be re-written. The 80/20 rule will invariably apply -- 80% of the execution time will be spent in 20% of the code -- so at a minimum just re-write the 20% of the code that's executed on the most frequent paths. Leave the rest alone. Re-writing it will just be a waste of time, and you have to fix all the old bugs that were re-introduced during the re-write.

Basically, Joel's take on a similar problem is: don't do it.

Unless you have a _really_ good reason to do huge change to a big codebase, don't bother, and make something more productive instead.