Extensions with constraints in Swift - Mini Project: Build & Apply

Extensions with constraints

📖 Scenario: You are building a simple app that works with collections of numbers. You want to add a new feature to calculate the sum of all elements, but only for collections that hold numbers.

🎯 Goal: Create an extension with constraints to add a sumElements() method to collections of numbers.

📋 What You'll Learn

Create an array of integers called numbers with the values [3, 7, 2, 9].

Create a constant called isNonEmpty that checks if numbers is not empty.

Write an extension for Collection where the element type is Int to add a method sumElements() that returns the sum of all elements.

Print the result of calling sumElements() on numbers.

💡 Why This Matters

🌍 Real World

Extensions with constraints let you add useful features to existing types only when they meet certain conditions, like holding numbers. This helps keep your code safe and organized.

💼 Career

Understanding how to write constrained extensions is important for Swift developers to create reusable and type-safe code, a common task in app development.

1

Create the initial array

Create an array called numbers with the exact values [3, 7, 2, 9].

Swift

# Create the array 'numbers' with values [3, 7, 2, 9]
# Your code here

Need a hint?

Use let numbers = [3, 7, 2, 9] to create the array.

2

Add a configuration constant

Create a constant called isNonEmpty that is true if numbers is not empty, otherwise false.

Swift

let numbers = [3, 7, 2, 9]
# Create 'isNonEmpty' to check if 'numbers' is not empty
# Your code here

Need a hint?

Use !numbers.isEmpty to check if the array is not empty.

3

Write the extension with constraints

Write an extension for Collection where the element type is Int. Add a method called sumElements() that returns the sum of all elements using reduce(0, +).

Swift

let numbers = [3, 7, 2, 9]
let isNonEmpty = !numbers.isEmpty

# Write an extension for Collection where Element == Int
# Add method sumElements() that returns the sum of elements
# Your code here

Need a hint?

Use extension Collection where Element == Int and reduce(0, +) inside sumElements().

4

Print the sum of elements

Print the result of calling sumElements() on the numbers array.

Swift

let numbers = [3, 7, 2, 9]
let isNonEmpty = !numbers.isEmpty

extension Collection where Element == Int {
    func sumElements() -> Int {
        return self.reduce(0, +)
    }
}

# Print the sum of elements in numbers
# Your code here

Need a hint?

Use print(numbers.sumElements()) to display the sum.