Kotlin - data classes - Dealing with Data - equals function、copy function、==operator、===operator

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 7(data classes - Dealing with Data)、Mixed Massages(203)の解答を求めてみる。

コード

data class Movie(val title: String, val year: String)
class Song(val title: String, val artist: String)

fun main() {
    var m1 = Movie("Black Panther", "2018")
    var m2 = Movie("Jurassic World", "2015")
    var m3 = Movie("Jurassic World", "2015")
    var s1 = Song("Love Cats", "The Cure")
    var s3 = Song("Love Cats", "The Cure")

    println((m2 == m3) == true)
    println((s1 == s3) == false)
    var m4 = m1.copy()
    println((m1 == m4) == true)
    var m5 = m1.copy()
    println((m1 === m5) == false)
    var m6 = m2
    m2 = m3
    println((m3 == m6) == true)
}

入出力結果

true
true
true
true
true

Process finished with exit code 0