Weak references to break cycles in Swift - Mini Project: Build & Apply

Weak references to break cycles

📖 Scenario: Imagine you are building a simple app to manage a library system. You have Book and Author classes. Each book has an author, and each author has a list of books they wrote. This creates a cycle in memory references.To prevent memory leaks, you need to use weak references in Swift.

🎯 Goal: You will create Book and Author classes with properties referencing each other. Then, you will use a weak reference to break the cycle and print the author and book details.

📋 What You'll Learn

Create a class Author with a name property and a books array property.

Create a class Book with a title property and an author property.

Make the author property in Book a weak reference to avoid a strong reference cycle.

Create instances of Author and Book and link them.

Print the author name and the titles of their books.

💡 Why This Matters

🌍 Real World

In real apps, especially with user interfaces and data models, objects often reference each other. Using weak references prevents memory leaks and keeps the app efficient.

💼 Career

Understanding how to manage memory with weak references is essential for Swift developers to write safe and performant code, especially in iOS app development.

1

Create the Author and Book classes

Create a class called Author with a name property of type String and a books property which is an array of Book. Also create a class called Book with a title property of type String and an author property of type Author? (optional).

Swift

# Your code here

Need a hint?

Define two classes with the properties exactly as described. Use optional type for author in Book.

2

Make the author property weak to avoid cycles

Change the author property in the Book class to be a weak reference of type Author?.

Swift

class Author {
    let name: String
    var books: [Book] = []
    
    init(name: String) {
        self.name = name
    }
}

class Book {
    let title: String
    // Make author a weak reference
    var author: Author?
    
    init(title: String, author: Author?) {
        self.title = title
        self.author = author
    }
}

Need a hint?

Use the weak keyword before the author property declaration.

3

Create instances and link them

Create an instance of Author named author with the name "Jane Austen". Create two Book instances named book1 and book2 with titles "Pride and Prejudice" and "Sense and Sensibility" respectively, and set their author property to the author instance. Add both books to the author.books array.

Swift

class Author {
    let name: String
    var books: [Book] = []
    
    init(name: String) {
        self.name = name
    }
}

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

// Create author and books, link them

Need a hint?

Create the instances exactly with the given names and values. Append the books to the author's books array.

4

Print author and book details

Write code to print the author's name and then print the titles of all books in the author.books array, each on a new line.

Swift

class Author {
    let name: String
    var books: [Book] = []
    
    init(name: String) {
        self.name = name
    }
}

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

let author = Author(name: "Jane Austen")
let book1 = Book(title: "Pride and Prejudice", author: author)
let book2 = Book(title: "Sense and Sensibility", author: author)
author.books.append(book1)
author.books.append(book2)

// Print author name and book titles

Need a hint?

Use print to show the author's name and then loop through author.books to print each book's title.