Destructuring Declarations

fun main() {
    val pair = "Kotlin" to 2011
    val (language, year) = pair
    println("$language was released in $year")
}

data class Point(val x: Int, val y: Int)

fun main() {
    val point = Point(3, 4)
    val (x, y) = point
    println("x=$x, y=$y")
}

fun main() {
    val scores = mapOf("Ana" to 90, "Bo" to 85)
    for ((name, score) in scores) {
        println("$name scored $score")
    }
}

data class Point3D(val x: Int, val y: Int, val z: Int)

fun main() {
    val point = Point3D(1, 2, 3)
    val (x, _, z) = point
    println("x=$x, z=$z")
}

1. Trying to destructure a regular class that has not declared componentN() functions (or is not a data class), which the compiler rejects.
2. Assuming destructuring order is based on property names; it is actually based on declaration order via component1(), component2(), etc.
3. Using _ unnecessarily verbosely instead of skipping an unwanted component with the underscore placeholder.

• val (a, b) = pair destructures an object into separate variables using its component1(), component2(), etc. functions.
• Data classes automatically provide componentN() functions for their constructor properties, making them destructurable out of the box.
• Pair and Map.Entry are standard library types that already support destructuring.
• An underscore _ can be used in place of a component you want to skip.