Destructuring Declarations

componentN Functions

A data class gets component1(), component2()... in the order of the constructor properties. They let you unpack an object into variables in one line.

Example

data class Employee(val name: String, val dept: String, val salary: Int)

fun main() {
    val e = Employee("Divya", "Android", 90000)
    val (name, dept, salary) = e
    println("$name works in $dept and earns $salary")
    println(e.component2())

    val (onlyName, _, pay) = e      // _ skips a value
    println("$onlyName -> $pay")
}

Output

Divya works in Android and earns 90000
Android
Divya -> 90000

Destructuring in Loops, Maps and Lambdas

Example

data class Score(val player: String, val runs: Int)

fun topScorer(scores: List<Score>): Pair<String, Int> {
    val best = scores.maxBy { it.runs }
    return best.player to best.runs          // Pair
}

fun main() {
    val scores = listOf(Score("Virat", 82), Score("Rohit", 45), Score("Gill", 104))
    for ((player, runs) in scores) println("$player: $runs")

    val (who, howMany) = topScorer(scores)
    println("Top scorer: $who ($howMany)")

    val capitals = mapOf("Telangana" to "Hyderabad", "Karnataka" to "Bengaluru")
    for ((state, city) in capitals) println("$state -> $city")
    capitals.forEach { (state, city) -> println("${state.take(3)}: $city") }
}

Output

Virat: 82
Rohit: 45
Gill: 104
Top scorer: Gill (104)
Telangana -> Hyderabad
Karnataka -> Bengaluru
Tel: Hyderabad
Kar: Bengaluru

Note: Pair and Triple are ready-made data classes. Use them for quick returns, but create a named data class when the meaning matters (Score is clearer than Pair<String, Int>).

Exercise

Exercise: Write a function minMax(list: List<Int>) that returns a Pair of the smallest and largest numbers, then destructure the result.

Show answer

fun minMax(list: List<Int>) = list.min() to list.max()

fun main() {
    val (lo, hi) = minMax(listOf(7, 2, 9, 4))
    println("min=$lo max=$hi") // min=2 max=9
}