The Maintenance Myth
Being a language geek, I tend to get into lots of discussions about the differences between languages, what’s good and what’s bad. And being a Ruby guy that hangs out in Java crowds, I end up having the static-vs-dynamic conversation way too often. And it’s interesting, the number one question everyone from the static “camp” has, the one thing that worries them the most is maintenance.
The question is basically - not having types at compile time, won’t it be really hard to maintain your system when it grows to a few millions of lines of code? Don’t you need the static type hierarchy to organize your project? Don’t you need an IDE that can use the static information to give you intellisense? All of these questions, and many more, boil down to the same basic idea: that dynamic languages aren’t as maintainable as static ones.
And what’s even more curious, in these kind of discussions I find people in the dynamic camp generally agrees, that yes, maintenance can be a problem. I’ve found myself doing the same thing, because it’s such a well established fact that maintenance suffers in a dynamic system. Or wait… Is it that well established?
I’ve asked some people about this lately, and most of the answers invariably beings “but obviously it’s harder to maintain a dynamic system”. Things that are “obvious” like that really worries me.
Now, Java systems can be hard to maintain. We know that. There are lots of documentation and talk about hard to maintain systems with millions of lines of code. But I really can’t come up with anything I’ve read about people in dynamic languages talking about what a maintenance nightmare their projects are. I know several people who are responsible for quite large code bases written in Ruby and Python (very large code bases is 50K-100K lines of code in these languages). And they are not talking about how they wish they had static typing. Not at all. Of course, this is totally anecdotal, and maybe these guys are above your average developer. But in that case, shouldn’t we hear these rumblings from all those Java developers who switched to Ruby? I haven’t heard anyone say they wish they had static typing in Ruby. And not all of those who migrated could have been better than average.
So where does that leave us? With a big “I don’t know”. Thinking about this issue some more, I came up with two examples where I’ve heard about someone leaving a dynamic language because of issues like this. And I’m not sure how closely tied they are to maintenance problem, not really, but these were the only ones I came up with. Reddit and CDBaby. Reddit switched from Lisp to Python, and CDBaby switched from Ruby to PHP. Funny, they switched away from a dynamic language - but not to a static language. Instead they switched to another dynamic language, so the problem was probably not something static typing would have solved (at least not in the eyes of the teams responsible for these switches, at least).
I’m not saying I know this is true, because I have no real, hard evidence one way or another, but to me the “obvious” claim that dynamic languages are harder to maintain smells a bit fishy. I’m going to work under the hypothesis that this claim is mostly myth. And if it’s not a myth, it’s still a red herring - it takes the focus away from more important concerns with regard to the difference between static and dynamic typing.
I did a quick round of shouted questions to some of my colleagues at ThoughtWorks I know and respect - and who was online on IM at the mime. The general message was that it depends on the team. The people writing the code, and how they are writing it, is much more important than static or dynamic typing. If you make the assumption that the team is good and the code is treated well from day 0, static or dynamic typing doesn’t make difference for maintainability.
Rebecca Parsons, our CTO said this:
I think right now the tooling is still better in static languages. I think the code is shorter generally speaking in dynamic languages which makes it easier to support.
I think maintenance is improved when the cognitive distance between the language and the app is reduced, which is often easier in dynamic languages.
In the end, I’m just worried that everyone seems to take the maintainability story as fact. Has there been any research done in this area? Smalltalk and Lisp has been around forever, there should be something out there about how good or bad maintenance of these systems have been. There are three reasons I haven’t seen it:
- It’s out there, but I haven’t looked in the right places.
- There are maintenance problems in all of these languages, but people using dynamic languages aren’t as keen on whining as Java developers.
- There are no real maintenance problems with dynamic languages.
There is a distinct possibility I’ll get lots of anecdotal evidence in the comments on this post. I would definitely prefer fact, if there is any to get.