Unowned references for guaranteed lifetime in Swift - Mini Project: Build & Apply

Unowned References for Guaranteed Lifetime in Swift

📖 Scenario: Imagine you are building a simple app to manage a library. Each Book has an Author. The Author always exists as long as the Book exists, so you want to link them without creating a strong reference cycle.

🎯 Goal: You will create two classes, Author and Book, and use an unowned reference in Book to refer to its Author. This ensures the Author will always be alive while the Book exists, avoiding memory leaks.

📋 What You'll Learn

Create a class called Author with a name property.

Create a class called Book with a title property and an unowned reference to an Author.

Initialize Book with a title and an Author.

Print the book's title and its author's name.

💡 Why This Matters

🌍 Real World

In real apps, classes often refer to each other. Using <code>unowned</code> references helps manage memory safely when one object always exists as long as the other does.

💼 Career

Understanding memory management and reference types in Swift is important for building efficient iOS apps without memory leaks.

1

Create the Author class

Create a class called Author with a name property of type String. Initialize name using an initializer.

Swift

# Your code here

Need a hint?

Think of Author as a simple class holding the author's name.

2

Create the Book class with an unowned reference

Create a class called Book with a title property of type String and an unowned property called author of type Author. Initialize both properties using an initializer.

Swift

class Author {
    let name: String
    
    init(name: String) {
        self.name = name
    }
}

# Your code here

Need a hint?

Use unowned before the author property to avoid strong reference cycles.

3

Create instances of Author and Book

Create an instance of Author named author with the name "Jane Austen". Then create an instance of Book named book with the title "Pride and Prejudice" and the author instance you just created.

Swift

class Author {
    let name: String
    
    init(name: String) {
        self.name = name
    }
}

class Book {
    let title: String
    unowned let author: Author
    
    init(title: String, author: Author) {
        self.title = title
        self.author = author
    }
}

# Your code here

Need a hint?

Create the author first, then pass it to the Book initializer.

4

Print the book title and author name

Print the book's title and its author's name in the format: "Pride and Prejudice by Jane Austen" using the book instance.

Swift

class Author {
    let name: String
    
    init(name: String) {
        self.name = name
    }
}

class Book {
    let title: String
    unowned let author: Author
    
    init(title: String, author: Author) {
        self.title = title
        self.author = author
    }
}

let author = Author(name: "Jane Austen")
let book = Book(title: "Pride and Prejudice", author: author)

# Your code here

Need a hint?

Use string interpolation to combine book.title and book.author.name.