Kotlin - abstract classes and interfaces - Serious Polymorphism - is operator, when

Head First Kotlin
A Brain-Friendly Guide
楽天ブックス(Kobo) 紀伊國屋書店(Kinoppy)

開発環境

• macOS Mojave - Apple (OS)
• Windows 10 Pro (OS)
• IntelliJ IDEA CE(Community Edition) (IDE(統合開発環境))
• Kotlin (プログラミング言語)

Head First Kotlin: A Brain-Friendly Guide (Dawn Griffiths(著)、David Griffiths(著)、O'Reilly Media)のChapter 6(abstract classes and interfaces - Serious Polymorphism)、BE the Compiler(187)の解答を求めてみる。

コード

interface Flyable {
    val x: String
    fun fly() = println("$x is flying")
}

class Bird : Flyable {
    override val x = "Bird"
}

class Plane : Flyable {
    override val x = "Plane"
}

class Superhero : Flyable {
    override val x = "Superhero"
}

fun main() {
    val f = arrayOf(Bird(), Plane(), Superhero())
    var x = 0
    while (x in 0..2) {
        when (f[x]) {
            is Bird -> {
                x++
                f[x].fly()
            }
            is Plane, is Superhero -> f[x].fly()
        }
        x++
    }
    x = 0
    while (x in 0..2) {
        val y = when (f[x]) {
            is Bird -> false
            else -> true
        }
        if (y) {
            f[x].fly()
        }
        x++
    }

    for (t in f) {
        if (t is Plane || t is Superhero) t.fly()
    }
}

入出力結果

Plane is flying
Superhero is flying
Plane is flying
Superhero is flying
Plane is flying
Superhero is flying

Process finished with exit code 0