Yes, it is my opinion, and yes, it might seem like a hate-post. But I’ll try to address the issues I have with Scala and its surroundings. I have used Scala in a single, relatively small project (currently working in production), so I guess I’m somewhere between “n00b” and “intermediate”.
- there are multiple right ways to do the same thing – there are a lot of tasks that you can achieve with one or two lines in Scala. But often there is more than one way to do it, and there’s no obvious winner. The options vary on the brevity-readability scale, on the functional-imperative scale, and in many other ways. I know what currying, partial functions, partially applied functions, folding, collect, map, apply, etc. do, but given a simple task I can use all of them I don’t know which one. Probably because I’m a beginner – true, and over time I guess I’ll build a preferred set of approaches. Which will likely differ from those of any other co-worker, and the projects will me “messy”. It would be something like having half the project with curly brackets on same line, and the other half – on the next line.
- it’s cryptic – you can probably be ok with all the symbols flying around after some coding, but I find it plain ugly. It is a high-level language and the use of so many symbols is troublesome. Take a look at this stackoverflow question to see what I mean.
- binary incompatibilities – I have an error that in a Scala 2.10 project I can’t use a library compiled with Scala 2.9. There are reasons for that, and it will probably be improved or completely fixed in the future, but for now it’s making life harder.
- not smoothly integrating with existing java frameworks and tools – this is partly due to the different mode of thinking (e.g. you may not need a DI framework in Scala), and there are already a couple of viable Scala alternatives (e.g. ORMs), but sometimes you would prefer to use proven technologies that you are familiar with. And it’s not only frameworks, but tools as well – I found it a nightmare to serialize JSON 6 months ago. All options had at least one thing that isn’t working as I need it, or lack a feature I need (both the java ones, the Java-Scala bridges, and the native Scala ones). I ended up using an abandoned project (jerkson). Luckily, the jackson support is now fixed (at least for my use-cases) and I switched to it. The same probably goes for other libraries as well.
- random failures – the time I’ve wasted in random things that break during compilation is significant. I only remember the last example, where I extended some Java class and I got an “AssertionError”, with some extra information that I don’t think makes sense to anyone, other than the author of the compiler. This particular example is related to the previous point (as I extended a Java class), but there are some more that I don’t remember, because they were random.
- irrelevant compiler errors – this isn’t universal, but sometimes you get a compiler errors that are not at all related to the actual problem.
- slow compilation – I haven’t really experienced that to a significant extent, since the project was small, but worth mentioning – see here
- IDEs used to be terrible. The scala-ide I’m using is from 6 months ago, and it is practically unusable – refactoring doesn’t work, inspection in debugging doesn’t work, sometimes compilation doesn’t work (while at the same time the maven build runs fine and classes are compiled). I tried IntelliJ back then, and it was slightly better, but I somehow didn’t always compile on save. Now the newest IntelliJ plugin works way better, and I’d say is actually usable. Probably the same goes for the eclipse-based scala-ide. So things are improving indeed, but used to be horrible at a time where you’d expect a technology to be more mature. And no, I don’t want to use vim/emacs/jedit/whatever for a statically-typed language that allows for refactoring, call hierarchies, etc.
- annotations, enums, reflection – coming from Java, I “cherish” these things. And while if you are in a pure Scala thinking, you may not need runtime retention of annotations, I still haven’t reached that Nirvana, and I also need to use it in conjunction with Java libraries. The workaround is to define java annotations in your project, alongside the Scala classes. Enums – I just don’t like the way they are defined, it’s unnecessarily verbose. And reflection is coming to Scala, but things like @ScalaSignature(bytes) scare me a bit.
- steep learning curve – even if you are familiar with functional programming, scala introduces a lot of stuff, including the “cryptic” symbols mentioned above. Not only that, but in order to get a full-featured scala project, you may need to learn a myriad or new frameworks and tools, like scalate, scalatest, Squeryl, etc. Partly because the Java-alternatives don’t work well with Scala, partly because the Scala alternatives are taking advantage of Scala features.
I’m not saying you shouldn’t use Scala. And obviously I haven’t listed all the good things about it. But for now I don’t like working with it – I am less productive due to the above problems that I would be in Java, and for me that trumps the productivity benefits that come from the cool language features. Things are obviously improving (both IDEs, the language, the runtime and the libraries), and I certainly don’t regret doing the project in Scala, as this is invaluable knowledge that I’ll possibly use later on.