[kcorbitt]

I've been using Kotlin on Android for about six months, and can't recommend it highly enough. If you're stuck in the Java ecosystem, Kotlin will make your life much better.

I also recommend it for people coming from the world of dynamic typing (Ruby, Javascript, Python, etc.). If you can appreciate the guarantees of a static type system -- and I submit that anyone who has worked on a project of more than a few KLOC can -- give Kotlin a try. It's much less verbose than Java, and gives you the tools and constructs to program in much the same style as you would in a dynamic language, but with extremely good compile-time correctness checks. It may not be Haskell, but it's pragmatic, practical and productive.

The tooling is also world class, as you might expect from a language developed by JetBrains. I recommend using Kotlin with IntelliJ -- the intellisense is guaranteed to boost your productivity.

Seamless Java interop has been a huge priority for the developers, so the ecosystem is also quite good. Its biggest weakness (for my use case anyway) is the lack of a good, modern web framework. Hopefully now that Kotlin is more stable a native library ecosystem will emerge that plays to Kotlin's strengths more than Java's.

[cartoonfoxes]

The language is promising, but given the incredibly fucked-up state of the Android build tooling merely getting to the point where you can evaluate Kotlin is an exercise in extreme patience.

> The tooling is also world class, as you might expect from a language developed by JetBrains. I recommend using Kotlin with IntelliJ -- the intellisense is guaranteed to boost your productivity.

It's a sad state when IntelliJ can be considered "world class". Sadly, I've had nearly as many problems with it as I have with Eclipse. I've been thrashing about desperately trying to find any production-ready alternatives to straight Java for Android development. I will literally cry tears of joy when I do, but it's not going to be today.

[Nilzor]

How does it affect built time and the feedback cycle?

[jinst8gmi]

Build times are supposed to be comparable to Java.

[zserge]

Build times are used to be slower, but I think recent Kotlin compilers have "daemon" mode to speed things up.

I personally use Kotlin on a daily basis for Android development and build time is comparable to the one of Java. May I also recommend Anvil framework (https://github.com/zserge/anvil)? It brings declarative layouts and data bindings, which works best with the immutable data types of Kotlin (much like React does in the web).

[kcorbitt]

I also highly recommend Anvil. Anvil + Kotlin makes Android development feel sane and at times even joyous! I should write a blog about my experiences.

[dodyg]

It's slower.

[mike_hearn]

It depends how you use it.

At the moment the gradle plugin doesn't do incremental compilation. If you use it for Android, that's an issue because of the Android build system.

I use Kotlin for free standing programs that run on my laptop/desktop. In these cases it's about as fast as Java, but that's because IntelliJ controls the compilation itself and gradle/maven is used only rarely.