Kotlin/Native Tech Preview: Kotlin without a VM

Andrey Breslav

We are happy to announce the first Technology Preview of Kotlin/Native that compiles Kotlin directly to machine code. The Kotlin/Native compiler produces standalone executables that can run without any virtual machine.

It is not a fully functional release yet, but you can already play with the technology and take a look at its source code here. The compiler is available under the Apache 2 OSS license.

Mission

Kotlin/Native is another step toward making Kotlin usable throughout a modern application. Eventually, it will be possible to use Kotlin to write every component, from the server back-end to the web or mobile clients. Sharing the skill set is one big motivation for this scenario. Another is sharing actual code.

Our vision for inter-platform code reuse is the following: one can write entire modules in Kotlin in a platform-independent way and compile them for any supported platform (currently these are Kotlin/JVM, Kotlin/JS and the upcoming Kotlin/Native). We call these common modules. Parts of a common module may require a platform-specific implementation, which can be developed individually for each platform. Common modules provide a common API for all clients, but other (platform-specific) modules can extend this API to provide some exclusive capabilities on their platform.

Note that we do not intend to make arbitrary Kotlin/JVM programs runnable on Kotlin/Native or Kotlin/JS. It would be equivalent to implementing another JVM, which is both a lot of work and a lot of limitations for the runtime. We are going another way: providing a common language for all platforms while enabling creation of common libraries through seamless interoperability with platform code.

Technology

Kotlin/Native uses the LLVM compiler infrastructure to generate machine code. In this preview, we support the following target platforms:

• Mac OS X 10.10 and later (x86-64)
• x86-64 Ubuntu Linux (14.04, 16.04 and later), other Linux flavours may work as well
• Apple iOS (arm64), cross-compiled on MacOS X host
• Raspberry Pi, cross-compiled on Linux host

More platforms can be added relatively easily, as long as the LLVM support is available for them. We will probably support a few more platforms out-of-the-box in the future.

As usual, interoperability is among our top priorities, and Kotlin/Native can efficiently call C functions and pass/get data to/from them. You can generate Kotlin bindings from a C header files at build time and get fast type-safe access to any API native to the target platform. See detailed instructions here.

Memory management

Kotlin/Native is designed to potentially enable different memory management solutions for different target platforms. For example, in the future it may make sense to have a tracing GC for server/desktop platforms, while ARC makes a lot more sense on iOS. Some platforms may only need manual memory management, and get an even smaller Kotlin/Native runtime in return.

This Technology Preview features automatic reference counting with a cycle collector on top, but what the final memory management solution(s) will look like is unknown at this point.

Current limitations

As mentioned above, Kotlin/Native is far from complete, so this Technology Preview has a number of limitations that will be eliminated at later stages:

• No performance optimization has been done yet, so benchmarking Kotlin/Native makes no sense at this point.
• The Standard Library and reflection support are far from complete, more APIs will be added later.
• Read more in the Release Notes.

Future plans

We are currently working on the core technology for Kotlin/Native which is the same for all target platforms (compiler, core runtime and library). As a matter of possible future work, we are considering the following possible use cases:

• iOS applications (reusing code with Android)
• Embedded systems/IoT (e.g., Arduino and beyond)
• Data analysis and Scientific Computing
• Server-side and Microservices (low-footprint executables, utilizing the power of coroutines)
• Game Development

How to try

We’ve prepared two archives with compiler, samples and documentation: for Mac and iOS and for Linux and Raspberry Pi.

Check out the Github project and Release Notes for instructions.

Your feedback is very welcome in the #kotlin-native channel on our public Slack (Get your invite here.

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