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Improve Code by Removing It

17 Oct

I’ve started going through O’Reilly’s 97 Things Every Programmer Should Know, and I plan to post the best ones, the ones I think we do a great job of following at Grooveshark and the ones I wish we did better, here at random intervals.

The first one is Improve Code by Removing It.

It should come as no surprise that the fastest code is code that never has to execute. Put another way, you can usually only go faster by doing less. And of course, code that never runs also exhibits no bugs. :)

Since I started at Groovshark, I’ve deleted a lot of code. 20% more code than I’ve ever written. More code than all but one of our developers has contributed. Despite that, I think we’ve only actually ever removed one feature, and we’ve added many more.

One of the things I see in the old code is an over enthusiastic attempt to make everything extremely flexible and adaptive. The original authors obviously made a noble effort to try to imagine every possible future scenario that the code might some day need to handle and then come up with an abstraction that could handle all of those cases. The problem is, those scenarios almost never come up. Instead, different features are requested which do not fit with the goals of the original abstraction at all, so then you end up having to work around it in weird ways that make the code more difficult to understand and less efficient.

Let me try to provide a more concrete example so you can see what I’m talking about. We have an Auth class that really only needs to handle 3 things:

  • Let users log in (something like Auth->login(username, password)
  • Let users log out (something like Auth->logout()
  • Find out who the logged in user is, if a user is logged in. (Auth->getUser())

Should be extremely straightforward, right? Well, the original author decided that the class should allow for multiple authentication strategies over various protocols in some scenarios that could never possibly arise (such as not having access to sessions) even though at the time only one was needed. Instead of ~100 lines of code to just get the job done and nothing else, we ended up with 1,176 lines spanning 5 files. The vast majority of that code was useless; our libraries are behind other front-facing code so the protocol and “strategy” for authenticating is handled at one level higher up, and we always use sessions so that no matter how a user logged in, they are logged in to all Grooveshark properties. When we finally did add support for a truly new way to log in (via Facebook Connect), none of that code was useful at all because Facebook Connect works in a way the author could never have anticipated 2 years ago. Finally, because the original author anticipated a scenario that cannot possibly arise (that we might know the user’s username but not their user ID), fetching the logged-in User’s information from the database required a less efficient lookup by username rather than a primary key lookup by ID.

Let’s step back a moment and pretend that the author had in fact been able to anticipate how we were going to incorporate Facebook Connect and made the class just flexible enough and just abstract enough in just the right ways to accommodate that feature that we just now got around to implementing. What would have been the benefit? Well, most of the effort of implementing that feature is handling all of the Facebook specific things, so that part would still need to be written. I’d say at best it could have saved me from having to write about 10 lines of code. In the meantime, we would have still been carrying around all of that extra code for no reason for a whole two years before it was finally needed!

Let’s apply YAGNI whenever possible, and pay the cost of adding features when they actually need to be added.

Edit:
Closely related: Beauty is in Simplicity.

 

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