Why Kotlin needs to bundle its runtime after compiled?

Question

I'm just trying to understand the underlying architecture, which I think I am getting wrong.

Taking the tutorial here as the example.

When I do:

kotlinc-jvm hello.kt -include-runtime -d hello.jar

Why it's needed to bundle the Kotlin runtime into the jar if the compiler already converted the code to Java bytecode?

question from:https://stackoverflow.com/questions/30565036/why-kotlin-needs-to-bundle-its-runtime-after-compiled

Answer 1

When you write an application in Java, you get to rely on all of the standard class libraries. The java. classes (e.g. java.lang.*, java.util.* ...) are included with every JRE, so you don't need to package them yourself.

Kotlin includes its own standard class library (the Kotlin runtime), separate to the Java class library. To distribute a jar file that can be run by anyone with a plain old JRE, you need to bundle the Kotlin runtime as well.

If you didn't bundle the Kotlin runtime, then your user would have to ensure the Kotlin runtime was on the classpath when executing your application. The page you linked gives an example of this scenario:

Compiling a library

If you’re developing a library to be used by other Kotlin applications, you can produce the .jar file without including the Kotlin runtime into it.

$ kotlinc-jvm hello.kt -d hello.jar

If you're targeting other Kotlin users, then its reasonable to assume they'll already have the Kotlin runtime available to them. However, if you're trying to deploy an application for an end-user, then you want to include the Kotlin runtime so that your application is self-contained.