Thoughts on (Programming) Scala

On a whim, I flew through Programming Scala this weekend. I’ve had the book for a while, and actively tried to read it before. But this time, it stuck.

All the ideas in Scala are fascinating for a language nerd. It’s the best instance I know of, so far, where ideas from object-oriented and functional programming are combined intentionally and at-scale to produce a language that developers are using on a day-to-day basis. For a language nerd like me, it’s fun to see how all those ideas play out together.

That said, there is a lot of language lawyering. Having to write a chapter on scoping and public/protected/private rules in OO seems like a demoralizing thing for the authors to tackle. And all those hybrid OO/FP ideas come at a conceptual cost; it seems like there’s a lot to know. I’ve noted before that I’m very interested to see how Scala does in the marketplace of minds. It’s a very large language, but I think it’s large in a way that is already familiar to developers. So it could end up that Scala isn’t a great beginner language, but is fine for someone who already knows one FP and one OO language.

I should note that this isn’t my first Scala rodeo. I’ve tried, at various times, to tinker and hack on little projects or simply to grok other people’s code. The blocker on these previous attempts is that I, personally, am sbt-challenged. Whenever I’ve tried to compile projects or add dependencies to my own, I end up in an sbt-shaped trough of disallusionment. Part of this is my ongoing war of attrition with Maven. Part of this is, well, I’m not sure yet. I should note that I can mostly make leiningen, also Maven-based, work. So it’s not entirely Maven’s fault.

Most interesting to me is that Scala could have the versatility of Ruby, wherein one can grow a program from a script, to a message-based program, to a hybrid OO/functional system, to a multi-machine distributed program. You can’t say this about other JVM languages like Java or Clojure. The JVM is a gift and a curse. It makes Scala and Java impractical for scripts, due to startup time. But once your program is somewhat grown-up, Hotspot and the JVM’s excellent concurrency features come in quite handy.

More specific to the book, it cleared up some ideas I’d previous found confusing:

  • What’s a method call/operator overloading? It’s an object, a dot or space, and then a method/operator name.
  • Implicit methods/views; if you declare methods with the implicit keyword and they have the right type signature, the compiler will use them to coerce objects to your own types, giving you many of the benefits of something like Ruby’s open classes
  • How functions, maps, and ad-hoc data structures that are typical in Ruby map to actual types in Scala; lots of things get converted to Function and Tuple objects by the compiler, which makes sense when you think about it in an ML-ish everything-is-strongly-typed way.
  • Internal DSLs feel weird, but parser combinators for external DSLs seems like it would be great.
  • for-comprehensions; I guess I’ve read enough about them in Clojure now that they make sense in Scala. It’s worth noting that Scala’s for-comprehensions feel simpler than Clojure’s.
  • Self-type annotations; I’ve seen this all over in Scala code and didn’t quite understand what was going on. It sure does have an odd name.

And some things are still confusing to me:

  • Type bounds, variance; when will I need these?
  • Linearization of object hierarchies; rules, I don’t like learning them!
  • Tail-calls/trampolines; the JVM makes this a headhurt.
  • Path-dependent types; not sure when I’d really need this, but it’s good to know about.
  • Anything that’s a band-aid over type-erasure; again, the JVM is sometimes a headhurt.

I don’t have any projects that imminently need the things that Scala provides. Further, I think imposing Scala on a team that’s already succeeding at Ruby or Python is a stretch. You have to be in a place where you really need low, predictable latencies to accept the tradeoff of working with a much larger language.

That said, it’s totally a reasonable choice as a way to get yourself onto the JVM; if Clojure isn’t your thing, Scala probably is. Even if neither are your thing, don’t be a wuss; read some code in either language and expand your mind to reduce your headhurt.

Adam Keys @therealadam