Example of when is construction in Kotlin

WhenIs.kt

import java.io.IOException
import java.net.UnknownHostException

open class Foo {}

class Bar: Foo() {}

fun getFooOrBar(fooOrBar: Foo): String {
    return when (fooOrBar) {
        is Foo -> "Foo"
        is Bar -> "Bar"
        else -> "Unknown"
    }
}

fun getMessageForException(exception: Throwable): String {
    return when (exception) {
        is IOException -> "IOException"
        is UnknownHostException -> "UnknownHostException"
        else -> "Exception"
    }
}

fun main(args: Array<String>) {
    println(getFooOrBar(Bar()))
    println(getMessageForException(UnknownHostException()))
}