Peter Seibel - Coders at Work - Reflections on the craft of programming

Then I was sending in patches to Gaim, the GTK instant-messenger thing, and I was digging around that code and I just saw the whole design. Just seeing parts of it, I understood. I realized, after looking at other people’s code, that it wasn’t that I memorized all my own code; I was starting to see patterns. I would see their code and I was like, “Oh, OK. I understand the structure that they’re going with.”

Then I really enjoyed reading code, because whenever I didn’t understand some pattern, I was like, “Wait, why the fuck did they do it like this?” and I would look around more, and I’d be like, “Wow, that is a really clever way to do this. I see how that pays off.” I would’ve done that earlier but I was afraid to do it because I was thinking that if it wasn’t my code, I wouldn’t understand it.

Seibel:And how do you tackle reading other people’s code? For starters, do you read code just to see how it works overall, or do you always go in with some change you want to make?

Fitzpatrick:Generally I wanted to change something. Or if you really respect some programmer, go read some of their code. Maybe that’ll make you realize that they’re mortal and they’re not really someone you should be idolizing. Or you learn something about their code.

Seibel:So say you’ve got a change you want to make; how do you tackle it?

Fitzpatrick:First step, take a virgin tarball or check out from svn, and try to get the damn thing to build. Get over that hurdle. That tends to be the hugest hurdle for most people—dependencies in the build system or they’re assuming this library is installed. I almost wish that these large projects just came with a virtual machine that was the build environment.

Seibel:You mean like a VMware virtual machine?

Fitzpatrick:Yeah, so if you just want to get into hacking on it really quickly, here’s all the dependencies. People’s connections are getting quick enough. That’s totally viable.

Anyway, once you have one clean, working build, kill it, and just make one damn change. Change the title bar to say, “Brad says, ‘Hello world.’” Change something. Even if everything’s ugly, just start making changes.

Then send out patches along the way. I find that’s the best way to start a conversation. If you get on a mailing list and you’re like, “Hey, I want to add a feature X,” the maintainer is probably going to be like, “Oh fuck, I’m so busy. Go away. I hate feature X.” But if you come to them and you’re like, “I want to add feature X. I was thinking something like the attached patch,” which is totally wrong but you say, “But I think it’s totally wrong. I’m thinking the right way might be to do X,” which is some more complex way, generally they’ll be like, “Holy crap, they tried, and look, they totally did it the wrong way.”

Maybe that pains the maintainer. They’re like, “Oh man, I can’t believe they went through all that effort to do it. It’s so easy to do it the right way.” Or, “Oh, wow, they did all this work in the wrong direction. I hope they don’t go in that direction any more.” And then they reply.

That’s always the best way to start a conversation. Even at Google, that’s the way I start a lot of conversations to a team I don’t know. When I fix a bug in their product the first thing I do is send them a patch in the mail and just say, “What do you guys think of this?” Or on the internal code-review tool I’d be like, “Here is a review. What do you think?” They could just say, “Fuck no, that’s totally the wrong fix.”

Seibel:Do you still read code for fun, as opposed to reading it because you need to work with it?

Fitzpatrick:Sometimes. I checked out Android source code for no real reason. The same with Chrome; when it went open source, I mirrored the repo and just looked around. I did the same thing with Firefox and Open Office. Some program you’ve been using and all of a sudden you have access and you might as well look.

Seibel:Programs like that, the code base is pretty huge. When you look at something like that for fun, how deeply do you get into it?

Fitzpatrick:Generally, I’ll just pipe findinto lessand try to understand the directory structure. Then either something grabs my eye or I don’t understand what something is. So I pick a random file and get a feel for it. Then I bounce around and wander aimlessly until I’m bored and then pick a new random spot to jump in.

A lot of times, I’ll work on building it in parallel with reading it because they’re very parallelizable tasks, especially if it’s hard to build. By the time it’s finally built, then I can start tweaking it if I want to.

Seibel:So when you read good code it either fits into patterns that you already understand, or you’d discover new patterns. But not all code is good. What are the first warning signs of bad code?

Fitzpatrick:Well, I’m particularly snooty now, having worked at Google with really strict style guidelines in all languages. On our top six or seven languages, there’s a really strict style guide that says, “This is how we lay out our code. This is how we name variables. This is how we do spacing and indentation, and these patterns and conventions you use, and this is how you declare a static field.”

We’ve started putting these online too, just as a reference for external contributors contributing to our projects. We wanted to have a documented policy so we don’t just say, “We don’t like your style.”

Now when I work on projects in C, the first thing I do is add a style guide. Once a project is mature and has a lot of people hacking on it, they’ll have a style guide. It’s not even always written, but the programmers just respect the style of code written already. Maybe they don’t like the brace style, but fuck it, it’s more important to have it consistent within a file, within a project, than to do it your favorite way.

Seibel:Do you ever do any pair programming?

Fitzpatrick:I think it’s pretty fun. It’s good for lots of things. Sometimes you just need to think and want to be left alone. I don’t subscribe to it all the time, but it’s definitely fun.

I start too many projects. I finish them because I have guilt if I don’t finish them, but I definitely context-switch way too often and I’m spread too thin. This is why I really need pair programming—it forces me to sit down for three solid hours, or even two or one solid hour, and work on one thing with somebody else, and they force me to not be bored. If I hit a bored patch, they’re like, “Come on. We’ve got to do it,” and we finish.

I like working alone but I just bounce all over the place when I do. On a plane I’ll bring extra laptop batteries and I have a whole development environment with local web servers and I’ll be in a web browser, testing stuff. But I’ll still be hitting new tabs, and typing “reddit” or “lwn”—sites I read. Autocomplete and hit Enter, and then—error message. I’ll do this multiple times within a minute. Holy fuck! Do I do this at work? Am I reading web sites this often that I don’t even think about it? It’s scary. I had a friend, who had some iptables rule, that on connection to certain IP addresses between certain hours of the day would redirect to a “You should be working,” page. I haven’t got around to doing that, but I need to do something like it, probably.

Seibel:What about code ownership? Is it important for people to own code individually or is it better for a team to share ownership?