Destructuring

Learn componentN and destructuring declarations.

componentN and destructuring

Data classes generate a componentN method per property: component1, component2 and so on. These methods, with a destructuring declaration, split properties into separate variables.

Example: val (x, y) = point. This line calls point.component1() and point.component2(), assigning the results to x and y. Standard classes like Pair and Triple support this pattern too. In loops it appears as for ((k, v) in map).

Destructuring in loops

Destructuring can be used in a for loop too. This is convenient to split the items of a list.

Example: for ((name, age) in users) { println("$name - $age") }. Each item in users is split into two components. List, Pair and Map.Entry support this pattern. You can skip a component with _: val (name, _) = user.

Exercise Destructuring with the Point data class

Define a data class named Point with a primary constructor taking val x: Int, val y: Int. In main create a Point(3, 4) instance and split it into a and b with destructuring. Print a and b separately with println.

Show example solution

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

fun main() {
    val p = Point(3, 4)
    val (a, b) = p
    println(a)
    println(b)
}

Test yourself

What does <code>val (a, b) = point</code> do?
- It splits point into a and b and errors out
- It calls point.component1() and component2() and assigns to a and b
- It deletes point
- It copies a and b into point
Show answer

It calls point.component1() and component2() and assigns to a and b — destructuring calls componentN methods.
Match the destructuring patterns

val (x, y) = p

Split into two
component1()

First property
val (n, _)

Skip the second
for ((k, v) in m)

Split in a loop

Complete the destructuring declaration

val p = Point(3, 4)
val ____ = p
println(a)
println(b)

Show answer

val p = Point(3, 4)
val (a, b) = p
println(a)
println(b)

Next lesson: Summary - Data class

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