Closures as function parameters in Swift - Mini Project: Build & Apply

Closures as function parameters

📖 Scenario: You are building a simple app that processes a list of numbers. You want to apply different operations to these numbers using small pieces of code called closures. Closures are like little helpers you can pass around to do tasks.

🎯 Goal: Learn how to pass closures as parameters to functions in Swift. You will create a function that takes a list of numbers and a closure to process each number. Then you will use this function with different closures to see different results.

📋 What You'll Learn

Create an array of integers named numbers with the values 1, 2, 3, 4, 5

Create a closure variable named multiplyByTwo that takes an Int and returns an Int by multiplying the input by 2

Create a function named processNumbers that takes an array of Int called nums and a closure parameter named operation of type (Int) -> Int, and returns an array of Int

Inside processNumbers, use a for loop to apply operation to each number in nums and collect the results in a new array

Call processNumbers with numbers and multiplyByTwo, then print the result

💡 Why This Matters

🌍 Real World

Passing closures as parameters is common in apps to customize behavior, like sorting lists, filtering data, or handling user actions.

💼 Career

Understanding closures and how to pass them to functions is essential for Swift developers working on iOS apps, enabling flexible and clean code.

1

Create the numbers array

Create an array called numbers with the exact values 1, 2, 3, 4, 5.

Swift

# Create the array 'numbers' with values 1, 2, 3, 4, 5
# Your code here

Need a hint?

Use square brackets [] to create an array and separate values with commas.

2

Create a closure to multiply by two

Create a closure variable named multiplyByTwo that takes an Int parameter called number and returns the number multiplied by 2.

Swift

let numbers = [1, 2, 3, 4, 5]
# Create the closure 'multiplyByTwo' that multiplies input by 2
# Your code here

Need a hint?

Use the syntax { parameter in expression } to create a closure.

3

Create the function that takes a closure

Create a function named processNumbers that takes two parameters: an array of Int called nums and a closure called operation of type (Int) -> Int. The function should return an array of Int. Inside the function, use a for loop with variable num to apply operation to each number in nums and collect the results in a new array called results. Return results at the end.

Swift

let numbers = [1, 2, 3, 4, 5]

let multiplyByTwo: (Int) -> Int = { number in
    return number * 2
}

# Create the function 'processNumbers' with parameters 'nums' and 'operation'
# Use a for loop with variable 'num' to apply 'operation'
# Collect results in 'results' array and return it
# Your code here

Need a hint?

Remember to create an empty array before the loop and append results inside the loop.

4

Call the function and print the result

Call the function processNumbers with the array numbers and the closure multiplyByTwo. Store the result in a variable called processedNumbers. Then print processedNumbers.

Swift

let numbers = [1, 2, 3, 4, 5]

let multiplyByTwo: (Int) -> Int = { number in
    return number * 2
}

func processNumbers(nums: [Int], operation: (Int) -> Int) -> [Int] {
    var results: [Int] = []
    for num in nums {
        results.append(operation(num))
    }
    return results
}

# Call 'processNumbers' with 'numbers' and 'multiplyByTwo'
# Store in 'processedNumbers' and print it
# Your code here

Need a hint?

Use let processedNumbers = processNumbers(nums: numbers, operation: multiplyByTwo) and then print(processedNumbers).