Ask HN: Has anyone here programmed in Kotlin? What do you think about it?
We built Roll for Android ( http://tryroll.com ) in Kotlin -- we currently have ~17k lines and have been working on it since this Spring.We wanted to iterate on a lot of the software structure we came up with for our Swift iOS app, and for a bunch of pieces we needed a powerful type system. So rather than just stick with Java -- as others have said, it's way too verbose, we started looking at alternatives. We wanted a strong type system. Scala has too much overhead for Android. Kotlin really stood out for us. This document by Jake Wharton at Square https://docs.google.com/document/d/1ReS3ep-hjxWA8kZi0YqDbEhC... made the decision easier. So we took the risk.And we love it!The best features:Null type safety!Lambdas can be inlined! No need to be afraid of anonymous inner class overhead on the map/filter/fold of iterables.Reified generics!Extension functions!Single-method interfaces/classes can be represented as lambdas!
aka  view.setOnClickListener(new View.OnClickListener() {
     @Override public void onClick(View v) { /* do something */ }
  });

becomes  view.setOnClickListener { /* do something */ }

This is great for things like RxJava.Speaking of which, the Java interoperability is fantastic. Any Android libraries we've tried work great from Kotlin.Using these tools, we've built a simple dependency injection framework, a handful of really useful extensions on things like T? (for example monadic bind), a hack for algebraic data types and pattern matching, and of course a fairly complex app.Android Studio's Kotlin support is fantastic (good job JetBrains!) -- it's a pleasure to use.I think Kotlin is totally worth using. The biggest issue for us is the build time. Our build takes anywhere from 1.5 to 6 minutes depending on how much you've changed, but I've found that the type system is strong enough that you don't have to do too many build-change a line-rebuild cycles.We'll be starting a blog soon to talk about some of the stuff we've been doing, but if you can't wait send me a message bkase at highlig.ht if you're interested in hearing more (I love talking about this stuff)