Function references (::functionName) in Kotlin - Mini Project: Build & Apply

Using Function References (::functionName) in Kotlin

📖 Scenario: You are building a simple Kotlin program that processes a list of numbers. You want to reuse existing functions by passing them as references instead of writing new code.

🎯 Goal: Learn how to use function references (::functionName) to pass functions as arguments and call them in Kotlin.

📋 What You'll Learn

Create a list of integers

Create a function that doubles a number

Use a function reference (::functionName) to apply the doubling function to each number in the list

Print the resulting list

💡 Why This Matters

🌍 Real World

Function references let you reuse existing functions easily when working with collections or callbacks, making your code cleaner and more readable.

💼 Career

Understanding function references is important for Kotlin developers to write concise and maintainable code, especially in Android app development and backend services.

1

Create a list of integers

Create a variable called numbers and assign it a list containing these integers: 1, 2, 3, 4, 5.

Kotlin

// Create a list called numbers with 1, 2, 3, 4, 5
// Your code here

Need a hint?

Use val numbers = listOf(1, 2, 3, 4, 5) to create the list.

2

Create a function that doubles a number

Create a function called double that takes an Int parameter named n and returns n * 2.

Kotlin

val numbers = listOf(1, 2, 3, 4, 5)

// Create a function called double that doubles an integer
// Your code here

Need a hint?

Define the function with fun double(n: Int): Int { return n * 2 }.

3

Use a function reference to apply doubling

Create a variable called doubledNumbers and assign it the result of calling numbers.map(::double) to apply the double function to each number.

Kotlin

val numbers = listOf(1, 2, 3, 4, 5)

fun double(n: Int): Int {
    return n * 2
}

// Use function reference ::double with map to create doubledNumbers
// Your code here

Need a hint?

Use val doubledNumbers = numbers.map(::double) to apply the function reference.

4

Print the resulting list

Write a println statement to display the doubledNumbers list.

Kotlin

val numbers = listOf(1, 2, 3, 4, 5)

fun double(n: Int): Int {
    return n * 2
}

val doubledNumbers = numbers.map(::double)

// Print doubledNumbers
// Your code here

Need a hint?

Use println(doubledNumbers) to show the doubled list.