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kotlinlang

We are building mobile SDK and one of our customers is using Kotlin. For me, it's the first day with Kotlin and after reading the documentation, I still don't understand how to run an example source code from a client.
In simplified form an example code looks like this:
```
extension SomeView {
    fun justPrintHello(){
        print("Hello")
    }
}
```
Are they trying to do something like `class OurCustomView extends ViewFromSdk` in the example?
What should I do to be able to run it for Android?
Sorry for maybe a naive questions )