Global actors (@MainActor) in Swift - Mini Project: Build & Apply

Using Global Actors with @MainActor in Swift

📖 Scenario: You are building a simple Swift program that manages a shared counter. This counter must be updated safely on the main thread to avoid conflicts in a user interface environment.

🎯 Goal: Learn how to use the @MainActor global actor to ensure that updates to a shared resource happen on the main thread.

📋 What You'll Learn

Create a class called Counter with a property value initialized to 0

Add a method increment() to increase value by 1

Mark the Counter class with the @MainActor attribute

Create an instance of Counter and call increment() three times

Print the final value of the counter

💡 Why This Matters

🌍 Real World

In apps with user interfaces, updating shared data on the main thread prevents crashes and keeps UI smooth.

💼 Career

Understanding @MainActor is important for Swift developers working on iOS/macOS apps to write safe, concurrent code.

1

Create the Counter class

Create a class called Counter with a property value set to 0.

Swift

# Your code here
// Create class Counter with value property

Need a hint?

Use class Counter { var value = 0 } to define the class and property.

2

Add increment() method

Add a method called increment() inside the Counter class that increases value by 1.

Swift

class Counter {
    var value = 0
    // Add increment() method here
}

Need a hint?

Define func increment() { value += 1 } inside the class.

3

Mark Counter with @MainActor

Add the @MainActor attribute before the Counter class declaration to make it a global actor isolated class.

Swift

// Add @MainActor attribute before class declaration
class Counter {
    var value = 0
    func increment() {
        value += 1
    }
}

Need a hint?

Place @MainActor on the line above class Counter.

4

Use Counter and print value

Create an instance of Counter called counter. Call increment() three times on counter. Then print counter.value.

Swift

@MainActor
class Counter {
    var value = 0
    func increment() {
        value += 1
    }
}

// Create counter instance and increment 3 times
// Print the final value

Need a hint?

Use let counter = Counter(), call counter.increment() three times, then print(counter.value).