Kotlin Design Patterns and Best Practices/

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Type Checks and Casts

Type Checks and Casts

Learn about type checks and casting in Kotlin.

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While writing our code, we may often be inclined to check what type our object is using is, and cast it using as. As an example, let’s imagine we’re building a system for superheroes. Each superhero has their own set of methods:

interface Superhero
class Batman : Superhero {
    fun callRobin() {
        println("To the Bat-pole, Robin!")
    }
}
class Superman : Superhero {
    fun fly() {
        println("Up, up and away!")
    }
}
Defining classes Batman and Superman, both implement the Superhero interface

There’s also a function where a superhero tries to invoke their superpower:

fun doCoolStuff(s: Superhero) {
    if (s is Superman) {
        (s as Superman).fly()
    }
    else if (s is Batman) {
        (a as Batman).callRobin()
    }
}
Performing superhero specific action based on type

But ...