class Cat {
    fun purr() = println("Purr purr")
}

// *** before: ***
fun petOld(animal: Any) {
    val isCat = animal is Cat
    if (isCat) {
        // animal.purr()      // <- Error: Any has no purr(),
                              // the check stored in a variable was forgotten
        (animal as Cat).purr()
    }
}

// *** in version 2.0: ***
// the K2 compiler became the default one and remembers the check
// that was saved into a variable
fun pet(animal: Any) {
    val isCat = animal is Cat
    if (isCat) {
        animal.purr()         // animal is smart cast to Cat
    }
}

fun main() {
    petOld(Cat())
    pet(Cat())
}