Weak self and unowned self patterns in Swift - Mini Project: Build & Apply

Weak self and unowned self patterns

📖 Scenario: Imagine you are building a simple app that fetches user data asynchronously. You want to avoid memory leaks by using weak self and unowned self patterns inside closures.

🎯 Goal: Learn how to use weak self and unowned self inside closures to prevent strong reference cycles in Swift.

📋 What You'll Learn

Create a class called UserFetcher with a method to fetch user data asynchronously

Use a closure that captures self weakly

Use a closure that captures self unowned

Print the fetched user data inside the closure

💡 Why This Matters

🌍 Real World

Using weak and unowned self is important in iOS apps to prevent memory leaks when using closures for callbacks, animations, or network requests.

💼 Career

Understanding these patterns is essential for Swift developers to write safe, efficient, and leak-free code in real-world app development.

1

Create the UserFetcher class with a fetch method

Create a class called UserFetcher with a method fetchUserData() that takes a closure parameter called completion of type (String) -> Void. Inside the method, call completion with the string "User data loaded".

Swift

class UserFetcher {
    // Your code here
}

Need a hint?

Define a class and a method with a closure parameter. Call the closure with the given string.

2

Add a method using weak self in closure

Inside UserFetcher, add a method called loadUserDataWeak() that calls fetchUserData and uses a closure capturing self weakly. Inside the closure, unwrap self safely and print "Weak self: " followed by the data.

Swift

class UserFetcher {
    func fetchUserData(completion: (String) -> Void) {
        completion("User data loaded")
    }

    // Your code here
}

Need a hint?

Use [weak self] in the closure capture list and unwrap self with guard let.

3

Add a method using unowned self in closure

Inside UserFetcher, add a method called loadUserDataUnowned() that calls fetchUserData and uses a closure capturing self unowned. Inside the closure, print "Unowned self: " followed by the data.

Swift

class UserFetcher {
    func fetchUserData(completion: (String) -> Void) {
        completion("User data loaded")
    }

    func loadUserDataWeak() {
        fetchUserData { [weak self] data in
            guard let self = self else { return }
            print("Weak self: \(data)")
        }
    }

    // Your code here
}

Need a hint?

Use [unowned self] in the closure capture list and print directly without unwrapping.

4

Call both methods and print output

Create an instance of UserFetcher called fetcher. Call fetcher.loadUserDataWeak() and fetcher.loadUserDataUnowned() to print the outputs.

Swift

class UserFetcher {
    func fetchUserData(completion: (String) -> Void) {
        completion("User data loaded")
    }

    func loadUserDataWeak() {
        fetchUserData { [weak self] data in
            guard let self = self else { return }
            print("Weak self: \(data)")
        }
    }

    func loadUserDataUnowned() {
        fetchUserData { [unowned self] data in
            print("Unowned self: \(data)")
        }
    }
}

// Your code here

Need a hint?

Create an instance and call both methods to see the printed output.