Higher-order function declaration in Kotlin - Mini Project: Build & Apply

Higher-order function declaration in Kotlin

📖 Scenario: Imagine you are building a simple calculator app that can perform different operations like addition and multiplication. You want to write a function that can take another function as input to decide which operation to perform.

🎯 Goal: Build a Kotlin program that declares a higher-order function which accepts two numbers and a function to perform an operation on those numbers.

📋 What You'll Learn

Create a higher-order function called calculate that takes two Int parameters and a function parameter that itself takes two Int and returns an Int.

Create two simple functions called add and multiply that each take two Int parameters and return their sum and product respectively.

Use the calculate function to perform addition and multiplication by passing add and multiply as arguments.

Print the results of both operations.

💡 Why This Matters

🌍 Real World

Higher-order functions are used in many apps to customize behavior, like sorting lists, handling user input, or performing calculations based on user choices.

💼 Career

Understanding higher-order functions is important for Kotlin developers because it helps write clean, reusable, and flexible code, which is highly valued in software development jobs.

1

Create the add and multiply functions

Write two functions called add and multiply. Each should take two Int parameters named a and b. The add function should return the sum of a and b. The multiply function should return the product of a and b.

Kotlin

# Your code here

Need a hint?

Define two functions with the exact names and parameters. Use return a + b for addition and return a * b for multiplication.

2

Declare the higher-order function calculate

Create a function called calculate that takes three parameters: two Int parameters named x and y, and a function parameter named operation which itself takes two Int parameters and returns an Int. The calculate function should return the result of calling operation(x, y).

Kotlin

fun add(a: Int, b: Int): Int {
    return a + b
}

fun multiply(a: Int, b: Int): Int {
    return a * b
}

# Your code here

Need a hint?

Define calculate with two Int parameters and one function parameter with type (Int, Int) -> Int. Return the result of calling operation(x, y).

3

Use calculate with add and multiply

Create two variables called sumResult and productResult. Assign sumResult the result of calling calculate with arguments 5, 3, and the add function. Assign productResult the result of calling calculate with arguments 5, 3, and the multiply function.

Kotlin

fun add(a: Int, b: Int): Int {
    return a + b
}

fun multiply(a: Int, b: Int): Int {
    return a * b
}

fun calculate(x: Int, y: Int, operation: (Int, Int) -> Int): Int {
    return operation(x, y)
}

# Your code here

Need a hint?

Use the function reference operator :: to pass add and multiply to calculate.

4

Print the results

Write two println statements to print sumResult and productResult.

Kotlin

fun add(a: Int, b: Int): Int {
    return a + b
}

fun multiply(a: Int, b: Int): Int {
    return a * b
}

fun calculate(x: Int, y: Int, operation: (Int, Int) -> Int): Int {
    return operation(x, y)
}

val sumResult = calculate(5, 3, ::add)
val productResult = calculate(5, 3, ::multiply)

# Your code here

Need a hint?

Use println(sumResult) and println(productResult) to show the results.