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

Seibel:How does that fit with your dismay at the Java guys who tell you, “Oh, Java takes care of that for you.” Isn’t that the same? “Well, App Engine will take care of that for you.”

Fitzpatrick:I don’t know. Maybe it’s because I know what’s going on. Actually the JVM isn’t that bad. I guess it’s when people have blind faith in their abstractions without understanding what’s going on.

Seibel:You had a lot of programming experience by the time you got to college and studied computer science. How did that work out?

Fitzpatrick:I skipped a lot of my early C.S. classes, because they were just really boring. I would go and take the tests. Then towards the end they got kind of fun, once you get to the 300- and 400-level classes. But right when it got interesting, I graduated. And they wouldn’t let me take the fun grad-level classes, because I wasn’t a grad student.

I remember in the compiler class, the final project was we had to take this existing language that we had been playing with and add a whole bunch of features, including one feature of our own choosing as the bonus part of the project. So I chose to implement run-time array bounds checking. Anyway, the professor took our compiled binary and ran his test suite against it, and it failed a couple of his tests. He was like, “Sorry, you get a C because you failed my unit test,” When I went to look at it, I was like, “You have off-by ones in your test suite.” So he gave me the grade back and I got an A, but I never got the bonus points for adding a feature to the language. I was angry at school at that point.

And I remember our database class was taught by someone who, it seemed, had no real-world experience with databases. At this point I’d worked with Oracle, Microsoft Server, and tons of MySQL. So I was asking all these realworld questions I actually wanted answers to—things that were melting right now—they would just give me some textbook answer. I’m like, “No, no. That doesn’t work.”

Seibel:You graduated in 2002. Do you have any greater appreciation now of what they were trying to teach you?

Fitzpatrick:Half the classes I totally loved, and either I learned something totally new that I wouldn’t have learned at the time, or I learned the proper background material and the proper terminology. Prior to that, I knew programming pretty well but I didn’t have the vocabulary to describe what it was I was doing. Or I would make up my own terminology for it and people would think I didn’t know what I was talking about. Formal C.S. education helped me be able to talk about it.

Seibel:Do you have any regrets about combining running a business with school? Would you rather have just done one or the other?

Fitzpatrick:No, I think that was the best way. I had friends who went to college and just did college, but I knew so much of it already, I would’ve been bored. I had one friend who also knew a whole bunch of it but he was of this school of thought that he’s at college to learn, not for grades, so he was, on the side, studying Arabic and Chinese and Japanese. And all the crazy programming languages. Every week it was like, “I have a new favorite language. This week I’m only going to write in OCaml.” So he kept himself busy that way. I kept myself busy and not bored other ways.

Then I had friends who dropped out after their freshman year just to do web stuff. A couple were doing a porn web site or something. They were like, “Oh, we’re making all this money.” But they just worked a whole bunch; they were always in their basement working. College was awesome for meeting people and partying. If I just did LiveJournal, I would’ve killed myself stresswise.

Seibel:Are you glad you studied computer science?

Fitzpatrick:I probably could have done without it. I did a lot of things I wouldn’t have done normally, so I guess it was good. I wish maybe I would have like done something else as well, maybe stayed another year and double-majored in something totally unrelated. Did linguistics more. I’m kind of sad I left college and I felt I only did half studying because so much of it I already knew. My early C.S. classes I barely attended and it was only towards the end where things just started to get interesting when it was like, “OK, you’re done.”

Seibel:Did you ever think about going to grad school?

Fitzpatrick:Yeah. It would have been fun, but I was busy.

Seibel:Do you try to keep up with the C.S. literature?

Fitzpatrick:Me and my friends still forward each other papers around, neat papers. I read something the other day about some new technique for resizing Bloom filters at runtime. It was pretty awesome. The papers that come out of the storage conferences, some out of industry and some from academics, about different cool systems—I try to read those. There are different reading groups at Google—systems reading groups or storage reading groups. I’ll see something on Reddit or a friend will forward a paper or something like that or link it on a blog.

Seibel:You just mentioned papers from the academy and from industry. Do you have any sense of whether those two meet in the right place these days?

Fitzpatrick:They kind of feel about the same to me. But it’s more interesting, a lot of times, to read the industry ones because you know they did it to solve a problem and their solution works as opposed to, “We’d think it would be cool if—” There’s a lot of crazier stuff that comes out of academia and it doesn’t actually work, so it’s just a crazy idea. Maybe they turn it into commercial things later.

Seibel:How do you design software?

Fitzpatrick:I start with interfaces between things. What are the common methods, or the common RPCs, or the common queries. If it’s storage, I try to think, what are the common queries? What indexes do we need? How are the data going to be laid out on disk? Then I write dummy mocks for different parts and flesh it out over time.

Seibel:Do you write mocks in the test-first sense so you can test it as you go?

Fitzpatrick:More and more. I always designed software this way, even before testing. I would just design interfaces and storage first, and then work up to an actual implementation later.

Seibel:What form would the design take? Pseudocode? Actual code? Whiteboard scribbles?

Fitzpatrick:Generally I would bring up an editor and just write notes with pseudocode for the schema. After it got good, I would make up a real schema and then I would copy-paste it in just to make sure that “create table” works. Once I got that all going, I’d actually go implement it. I always start with a spec.txt first.

Seibel:After you write a bunch of code do you ever discover that you really need to reconsider your original plan?

Fitzpatrick:Sometimes. But I’ve started with the hard bits or the parts I was unsure of, and tried to implement those parts first. I try not to put off anything hard or surprising to the end; I enjoy doing the hard things first. The projects that I never finish—my friends give me shit that it’s a whole bunch—it’s because I did the hard part and I learned what I wanted to learn and I never got around to doing the boring stuff.

Seibel:Do you have any advice for self-taught programmers?

Fitzpatrick:Always try to do something a little harder, that’s outside your reach. Read code. I heard this a lot, but it didn’t really sink in until later. There were a number of years when I wrote a lot of code and never read anyone else’s. Then I get on the Internet and there’s all this open source code I could contribute to but I was just scared shitless that if it wasn’t my code and the whole design wasn’t in my head, that I couldn’t dive in and understand it.