Why actors prevent data races in Swift - See It in Action

Why actors prevent data races

📖 Scenario: Imagine you have a shared bank account accessed by multiple people at the same time. Without rules, two people might try to withdraw money simultaneously, causing errors. In Swift, actors help manage this by making sure only one person accesses the account at a time, preventing mistakes called data races.

🎯 Goal: You will create a simple BankAccount actor that safely updates the balance. You will then try to update the balance from multiple tasks and see how actors prevent data races.

📋 What You'll Learn

Create an actor called BankAccount with a balance property set to 100

Add a function withdraw(amount:) inside the actor to subtract from balance

Create a constant account as an instance of BankAccount

Call withdraw(amount: 30) twice concurrently using Task

Print the final balance after both withdrawals

💡 Why This Matters

🌍 Real World

Actors are used in apps where multiple parts of the program need to safely share and update data, like bank apps, games, or messaging apps.

💼 Career

Understanding actors and data race prevention is important for Swift developers working on safe, concurrent applications.

1

Create the BankAccount actor with initial balance

Create an actor called BankAccount with a variable balance set to 100 inside it.

Swift

# Create the BankAccount actor with balance 100
# Your code here

Need a hint?

Use the actor keyword and define var balance = 100 inside it.

2

Add a withdraw function to the actor

Inside the BankAccount actor, add a function called withdraw(amount: Int) that subtracts amount from balance.

Swift

actor BankAccount {
    var balance = 100
    
    // Add withdraw(amount:) function here
    // Your code here
}

Need a hint?

Define a function withdraw(amount: Int) that reduces balance by amount.

3

Create an instance and withdraw concurrently

Create a constant account as an instance of BankAccount. Then start two concurrent Tasks that each call await account.withdraw(amount: 30).

Swift

actor BankAccount {
    var balance = 100
    
    func withdraw(amount: Int) {
        balance -= amount
    }
}

// Create account instance
// Start two concurrent tasks to withdraw 30
// Your code here

Need a hint?

Create let account = BankAccount() and use two Task blocks calling await account.withdraw(amount: 30).

4

Print the final balance after withdrawals

Add a Task that waits a moment and then prints await account.balance to show the final balance.

Swift

actor BankAccount {
    var balance = 100
    
    func withdraw(amount: Int) {
        balance -= amount
    }
}

let account = BankAccount()

Task {
    await account.withdraw(amount: 30)
}
Task {
    await account.withdraw(amount: 30)
}

// Add a Task to print the final balance
// Your code here

Need a hint?

Use Task.sleep to wait briefly, then print await account.balance.