Comment by cwyers
11 years ago
I love the parable of Chesterton's fence. And I feel it's very, very applicable to a lot of discussion I see here on HN (I feel like the rhetoric around Bitcoin vis a vis the current financial system could do with a good infusion of Chesterton's fence, for example, as could NoSQL/NewSQL databases.)
It's very applicable to software development in general. "Who wrote this crap? I'm rewriting it!"
Yeah, I'm reminded of Joel Spolsky's essay on Netscape and why rewriting from scratch is a bad idea:
http://www.joelonsoftware.com/articles/fog0000000069.html
"The idea that new code is better than old is patently absurd. Old code has been used. It has been tested. Lots of bugs have been found, and they've been fixed. There's nothing wrong with it. It doesn't acquire bugs just by sitting around on your hard drive. Au contraire, baby! Is software supposed to be like an old Dodge Dart, that rusts just sitting in the garage? Is software like a teddy bear that's kind of gross if it's not made out of all new material?
Back to that two page function. Yes, I know, it's just a simple function to display a window, but it has grown little hairs and stuff on it and nobody knows why. Well, I'll tell you why: those are bug fixes. One of them fixes that bug that Nancy had when she tried to install the thing on a computer that didn't have Internet Explorer. Another one fixes that bug that occurs in low memory conditions. Another one fixes that bug that occurred when the file is on a floppy disk and the user yanks out the disk in the middle. That LoadLibrary call is ugly but it makes the code work on old versions of Windows 95.
Each of these bugs took weeks of real-world usage before they were found. The programmer might have spent a couple of days reproducing the bug in the lab and fixing it. If it's like a lot of bugs, the fix might be one line of code, or it might even be a couple of characters, but a lot of work and time went into those two characters.
When you throw away code and start from scratch, you are throwing away all that knowledge. All those collected bug fixes. Years of programming work."
I find what Joel says problematic - firstly, you touch that code and you might break something, so it's fragile already, and secondly if it dealing with corner cases, then it should be documented.
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I feel like there's also a lesson here on the importance of commenting. If all of those inexplicable hairs had been properly commented, you wouldn't have to wonder.
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On that note though if you compare the old code to say a water pipe, the old code could be a pipe with tons of duct-tape over every leak and a new pipe could in fact be a good choice. It's not always a great idea to rewrite from scratch but it isn't always the best to keep old code around either.
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