Type checks and casts

In Kotlin, it’s common to check an object’s type using is and cast it using as. However, Kotlin’s smart casts simplify this process. Let’s consider an example with a superhero system:

interface Superhero
class Batman : Superhero {
    fun callRobin() {
        println("To the Bat-pole, Robin!")
    }
}
 
class Superman : Superhero {
    fun fly() {
        println("Up, up and away!")
    }
}
 
// Function invoking a superhero's power
fun doCoolStuff(s: Superhero) {
    if (s is Superman) {
        s.fly()
    } else if (s is Batman) {
        s.callRobin()
    }
}

Kotlin’s smart casting eliminates the need for explicit casting. The above function can be further optimized using when, producing cleaner code. However, it makes it necessary to handle the else case as long as it is not a sealed interface:

fun doCoolStuff(s: Superhero) {
    when(s) {
        is Superman -> s.fly()
       ...