KotlinNullable.md

Nullable

// Optional listener
listenerInterface?.notifyOfSomething()


// `elvis operator` ?: allows for default value
val likeCount = comment?.likes ?: 0


// Smart Cast
if(user != null) {
    user.foo() // compiler knows user isn't null, `?` isn't needed
} else {

}

// if-let
user?.let {
    it.foo()
}