Categorizing and understanding magical code

Sometimes, programmers like to disparage “magical code”. They say magical code is causing their bugs, magical code is offensive to use, magical code is harder to understand, we should try to write “less magical” code.

“Wait, what’s magic?”, I hear you say. That’s what I’m here to talk about! (Warning: this post contains an above-average density of “air quotes”, ask your doctor if your heart is strong enough for “humorous quoting”.)

Magic is code I have yet to understand

It’s not inscrutable code. It’s not bad code. It doesn’t intentionally defy understanding, like an obfuscated code contest or code golfing.

I can start to understand why a big of code is frustratingly magical to me by categorizing it. (Hi, I’m Adam, I love categorizing things, it’s awful.)

“Mathemagical” code escapes my understanding due to its foundation in math and my lack of understanding therein. I recently read Purely Functional Data Structures, which is a great book, but the parts on proving e.g. worst-case cost for amortized operations on data structures are completely beyond my patience or confidence in math. Once Greek symbols enter the text, my brain kinda “nope!”s out.

“Metamagic” is hard to understand due to use of metaprogramming. Code that generates code inside code is a) really cool and b) a bit of a mind exploder at first. When it works, its glorious and not “magical”. When it falls short, it’s a mess of violated expectations and complaints about magic. PSA: don’t metaprogram when you can program.

“Sleight of hand” makes it harder for me to understand code because I don’t know where the control flow or logic goes. Combining inheritance and mixins when using Ruby is a good example of control flow sleight-of-hand. If a class extends Foo, includes Bar, and all three define a method do_the_thing, which one gets called (trick question: all of them, trick follow-up question: in what order!)? The Rails router is a good example of logical sleight-of-hand. If I’m wondering how root to: “some_controller/index” works and I have only the Rails sources on me, where would I start looking to find that logic? For the first few years of Rails, I’d dig around in various files before I found the trail to that answer.

“Multi-level magic schemes” is my new tongue-in-cheek way to explain a tool like tmux. It’s a wonderful tool for those of us who prefer to work in (several) shells all day. I’m terrified of when things go wrong with it, though. To multiplex several shells into one process while persisting that state across user sessions requires tmux to operate at the intersection of Unix shells, process trees, and redrawing interfaces to a terminal emulator. I understand the first two in isolation, but when you put it all together, my brain again “nope!”s out of trying to solve any problems that arise. Other multi-level magic schemes include object-relational mappers, game engines, operating system containers, and datacenter networking.

I can understand magic and so can you!

I’m writing this because I often see ineffective reactions to “magical” code. Namely, 1) identify code that is frustrating, 2) complain on Twitter or Slack, 3) there is no step 3. Getting frustrated is okay and normal! Contributing only negative energy to the situation is not.

Instead, once I find a thing frustrating, I try to step back and figure out what’s going on. How does this bit of code or tool work? Am I doing something that it recommends against or doesn’t expect? Can I get back on the “golden path” the code is built for? Can I find the code and understand what’s going on by reading it? Often some combination of these side quests puts me back on my way an out of frustration’s way.

Other times, I don’t have time for a side quest of understanding. If that’s the case, I make a mental note that “here be dragons” and try to work around it until I’m done with my main quest. Next time I come across that mental map and remember “oh, there were dragons here!”, I try to understand the situation a little better.

For example, I have a “barely tolerating” relationship with webpack. I’m glad it exists, it mostly works well, but I feel its human factors leave a lot to be desired. It took a few dives into how it works and how to configure it before I started to develop a mental model for what’s going on such that I didn’t feel like it was constantly burning me. I probably even complained about this in the confidence of friends, but for my own personal assurances, attached the caveat of “this is magical because it’s unfamiliar to me.”

Which brings me to my last caveat: all this advice works for me because I’ve been programming for quite a while. I have tons of knowledge, the kind anyone can read and the kind you have to win by experience, to draw upon. If you’re still in your first decade of programming, nearly everything will seem like magic. Worse, it’s hard to tell what’s useful magic, what’s virtuous magic, and what’s plain-old mediocre code. In that case: when you’re confronted with magic, consult me or your nearest Adam-like collaborator.

Adam Keys @therealadam