Extension syntax in Swift - Mini Project: Build & Apply

Using Extension Syntax in Swift

📖 Scenario: Imagine you have a simple app that manages books. You want to add a new feature to calculate the age of a book since its publication without changing the original Book class.

🎯 Goal: Learn how to use extension syntax in Swift to add a new computed property to an existing class.

📋 What You'll Learn

Create a Book class with title and yearPublished properties

Add an extension to Book that adds a computed property age

Calculate the book's age based on the current year

Print the book's title and its age

💡 Why This Matters

🌍 Real World

Extensions let you add new features to existing code without changing it. This is useful when working with libraries or system classes.

💼 Career

Understanding extensions is important for Swift developers to write clean, modular, and maintainable code.

1

Create the Book class

Create a class called Book with two properties: title of type String and yearPublished of type Int. Initialize these properties with an initializer.

Swift

# Your code here

Need a hint?

Remember to define properties and an initializer inside the class.

2

Add an extension with a computed property

Add an extension to the Book class that adds a computed property called age of type Int. This property should calculate the difference between the current year (2024) and yearPublished.

Swift

class Book {
    let title: String
    let yearPublished: Int
    
    init(title: String, yearPublished: Int) {
        self.title = title
        self.yearPublished = yearPublished
    }
}

// Your code here

Need a hint?

Use extension Book { var age: Int { ... } } to add the computed property.

3

Create a Book instance and access age

Create a constant called myBook that is an instance of Book with the title "Swift Programming" and yearPublished 2015. Then, create a constant called bookAge that gets the age property from myBook.

Swift

class Book {
    let title: String
    let yearPublished: Int
    
    init(title: String, yearPublished: Int) {
        self.title = title
        self.yearPublished = yearPublished
    }
}

extension Book {
    var age: Int {
        return 2024 - yearPublished
    }
}

// Your code here

Need a hint?

Create the instance with Book(title: "Swift Programming", yearPublished: 2015) and access age.

4

Print the book's title and age

Write a print statement that outputs: "Swift Programming is 9 years old." using the title and bookAge variables with string interpolation.

Swift

class Book {
    let title: String
    let yearPublished: Int
    
    init(title: String, yearPublished: Int) {
        self.title = title
        self.yearPublished = yearPublished
    }
}

extension Book {
    var age: Int {
        return 2024 - yearPublished
    }
}

let myBook = Book(title: "Swift Programming", yearPublished: 2015)
let bookAge = myBook.age

// Your code here

Need a hint?

Use print("\(myBook.title) is \(bookAge) years old.") to show the message.