Destructuring Workbook

Practice problems for Destructuring: Unpacking an Object in One Line. Each takes a minute or two. Write your own answer first, then click Show answer — nothing here is a trick question, just direct practice of the syntax from the lesson.

the basics

1. Unpack a data class

Given data class User(val id: Int, val name: String) and val u = User(1, "Ada"), pull id and name into two variables in one line.

val (id, name) = u

2. What it expands to

The declaration val (id, name) = u is shorthand for what two calls?

val id = u.component1()
val name = u.component2()

3. Return two values

Write minMax(nums: List<Int>) returning a data class MinMax(val min: Int, val max: Int), then destructure the result at the call site.

data class MinMax(val min: Int, val max: Int)

fun minMax(nums: List<Int>) = MinMax(nums.min(), nums.max())

val (low, high) = minMax(scores)

loops and lambdas

4. Destructure map entries

Given a map ages, iterate it printing "<name> is <age>", destructuring each entry.

for ((name, age) in ages) {
    println("$name is $age")
}

5. Index and value

Iterate names with both the index and the value, destructured in the loop header.

for ((i, name) in names.withIndex()) {
    println("$i: $name")
}

6. Destructure a lambda parameter

Given val users = listOf(User(1, "Ada")), map each user to "<id>: <name>", destructuring the lambda parameter.

users.map { (id, name) -> "$id: $name" }

skipping and custom components

7. Skip a component

Given val u = User(1, "Ada"), bind only the name, ignoring the id.

val (_, name) = u

8. A List destructures too

Given val parts = "host=localhost".split("="), bind the two halves to key and value.

val (key, value) = "host=localhost".split("=")

9. Custom components

Add component1/component2 to class Pairish(val a: Int, val b: Int) so it can be destructured.

class Pairish(val a: Int, val b: Int) {
    operator fun component1() = a
    operator fun component2() = b
}

val (x, y) = Pairish(1, 2)

10. Destructure a Triple

Bind the three values of Triple(1, 2, 3) to a, b, and c in one line.

val (a, b, c) = Triple(1, 2, 3)

Back to the lesson, Destructuring, or on to the next one: visibility and packages.