Kotlin - a JVM language

I've been aware of the Kotlin JVM based language for a while, but hadn't taken a close look at it. I have to admit I thought it was odd for a new language to be coming from an IDE developer (Jetbrains). But who am I to talk about who should or shouldn't develop their own language :-)

I like Scala for its power, but the complexity (especially the type system) scares me. I like Xtend for its simplicity, but it's somewhat limited. Kotlin seems to be aiming for a sweet spot somewhere in between the two - more powerful than Xtend, but not as scary as Scala.

Here are a few of the things I like (in no particular order)

• optional semicolons
• var and val 
• modest type inference
• extension methods (like D and C# but more powerful)
  (I like this better than Scala's implicit conversions)
• traits (interfaces with method implementations)
• function literals aka lambdas or closures
• IDE support from the start
• improved handling of null references
• no checked exceptions
• standalone functions (everything doesn't have to be in a class)
• operator overloading
• infix function calls
• default and named arguments
• no "new" keyword
• when expressions
• static imports
• a goal of fast compilation
• good Java integration

There are a few more attractive features like inlining and runtime generics that are coming.

Of course, because it runs on the JVM and has good Java integration, I could mix Kotlin with Java in jSuneido. And I'd still have access to libraries like java.util.concurrent and Guava and ASM.

Another intriguing feature is that Kotlin can compile to JavaScript. I'm not sure why they're working on this, since their stated motivation for Kotlin is to have a better alternative to Java to write their IDE and other tools. Regardless, it's a neat idea. I've even had the crazy idea of implementing Suneido in JavaScript, but I'm not sure what the advantage would be, other than running in the browser. And I prefer statically typed languages for systems programming. I guess if I converted jSuneido to Kotlin, then in theory it could run in the browser (except for all the Java libraries I use).

I installed Jetbrains IntelliJ IDEA Community Edition (free) and added the Kotlin plugin. I've never really used IntilliJ but it wasn't hard to get started. Hello world was easy and so was implementing one of the classes I've been using for language evaluation. The Kotlin version of this class was the most clear and concise of the languages I've played with lately. (Without being so concise that it becomes cryptic.) I didn't have any installation problems or weird errors. Although this is beta software, it seems quite good.

I have mixed feelings about Kotlin arising from a commercial company. On the one hand it can mean there are some real resources behind it. And if Jetbrains really does use it for their own applications, then they will have a strong motivation to improve and polish it. (And hopefully less tendency to go down the rabbit hole of complexity.) On the other hand, a company can decide to drop projects for various business reasons. Thankfully, much of Kotlin is open source, so it has a life outside of just Jetbrains.

In a way I'm glad I didn't look into Kotlin when it was first announced (July 2011). Even now, it's still in beta and somewhat in flux. But it seems far enough along to play with and consider using at some point.

Hi, my name is Andrew, I'm a programming language addict ...