I would not recommend Scala anymore unless you're a small team with smart devs eager to learn it.
My project is not so small, and the average developer is not interested in spending the time to really learn the language and functional style.
So in the end, we have code that not everyone reads and writes well, an ecosystem that is years behind Java, and tons of incompatibilities between Scala versions as it's still not stable. It's a mess, and most just end up writing Scala imperatively a la Java from 2005.
Java 8 is actually pretty good and has a lot of the power of Java without the complex features few use correctly. I'm hoping Kotlin continues improving, too.
This was not my experience. Of course you need a team that has the drive to learn the language, whatever it is.
If you go out on your own and decide to build your project with Scala and a big focus on using a functional style but no one else is following, you are going to have a bad time.
I'd like to know what are your issues with Scala and versions because we don't have these. IMHO, Scala is years ahead of Java and it's possibly so different that comparing them does not even make sense.
The transition from Java to Scala is awkward because you can do most of the things you do with Java in Scala. With that said, I think it's counter productive to do it. Scala is very different and approaching it with an imperative Java (even an OO) style is the worst thing to do.
One thing that I realized is that some people can go off and write cryptic code in Scala, very easily. This is true of other languages as well but in Scala, you can do a lot of things that will make you regret it the next time you try to read the code.
The last problem we had was with various Fintatra / Finagle libraries written in 2.10.
We wanted to upgrade some other - not all - projects to newer versions of 2.11.
It wouldn't work because our Thrift clients were incompatible with stubs compiled with 2.10. We didn't have the time and manpower to rewrite all the dependent services, and so we're stuck on 2.10.
This is something that'd never happen with even old-school SOAP or similar web services. It kind of left a bad taste in my mouth.
Can you speak more specifically regarding the ecosystem being behind? I'm a recent addition to the Scala development world and love it. That being said I'm eager to listen to any opposing viewpoints.
My project is not so small, and the average developer is not interested in spending the time to really learn the language and functional style.
So in the end, we have code that not everyone reads and writes well, an ecosystem that is years behind Java, and tons of incompatibilities between Scala versions as it's still not stable. It's a mess, and most just end up writing Scala imperatively a la Java from 2005.
Java 8 is actually pretty good and has a lot of the power of Java without the complex features few use correctly. I'm hoping Kotlin continues improving, too.