Actor declaration syntax in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple actor named Logger.

Swift

actor [1] {
    func log(message: String) {
        print(message)
    }
}

Drag options to blanks, or click blank then click option'

Aenum Logger

Bclass Logger

Cstruct Logger

DLogger

Attempts:

3 left

💡 Hint

Common Mistakes

Using class, struct, or enum instead of actor.

In Swift, you declare an actor using the actor keyword followed by the actor's name.

2fill in blank

medium

Complete the code to declare an actor named DataStore with a property count initialized to 0.

Swift

actor DataStore {
    var count: Int = [1]
}

Drag options to blanks, or click blank then click option'

A0

Bnil

C"0"

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string "0" instead of the integer 0.

Using nil which is not valid for Int without optional.

The property count is an integer and should be initialized with the number 0.

3fill in blank

hard

Fix the error in the actor declaration by completing the code.

Swift

actor [1] {
    func fetchData() async -> String {
        return "Data"
    }
}

Drag options to blanks, or click blank then click option'

Afunc DataFetcher

BDataFetcher

Cclass DataFetcher

Dstruct DataFetcher

Attempts:

3 left

💡 Hint

Common Mistakes

Adding keywords like func or class before the actor name.

The actor name should be a simple identifier without keywords like func, class, or struct.

4fill in blank

hard

Fill both blanks to declare an actor named Counter with a method increment that increases count by 1.

Swift

actor [1] {
    var count = 0
    func [2]() {
        count += 1
    }
}

Drag options to blanks, or click blank then click option'

ACounter

BincrementCount

Cincrement

Dincrease

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that don't match increment behavior.

Using wrong actor names.

The actor is named Counter and the method to increase count is named increment.

5fill in blank

hard

Fill all three blanks to declare an actor named BankAccount with a balance property and a method deposit that adds amount to balance.

Swift

actor [1] {
    var [2]: Double = 0.0
    func [3](amount: Double) {
        balance += amount
    }
}

Drag options to blanks, or click blank then click option'

ABankAccount

Bbalance

Cdeposit

Dwithdraw

Attempts:

3 left

💡 Hint

Common Mistakes

Using withdraw instead of deposit for the method.

Using wrong property names.

The actor is BankAccount, the property is balance, and the method to add money is deposit.

Practice

1. What keyword is used to declare an actor in Swift?

easy

A. class

B. enum

C. struct

D. actor

Solution

1. Step 1: Understand actor declaration

   Actors in Swift are declared using a special keyword to indicate their concurrency-safe nature.

2. Step 2: Identify the correct keyword

   The keyword actor is used to declare actors, differentiating them from classes, structs, or enums.

3. Final Answer:

   actor -> Option D

4. Quick Check:

   Actor declaration keyword = actor [OK]

Hint: Actors always start with the keyword 'actor' [OK]

Common Mistakes:

• Using class instead of actor
• Confusing struct with actor
• Trying to declare actor with enum

2. Which of the following is the correct syntax to declare an actor named DataManager?

easy

A. actor DataManager() { }

B. actor DataManager { }

C. struct DataManager { }

D. class DataManager { }

Solution

1. Step 1: Recall actor declaration syntax

   Actors are declared with the keyword actor followed by the name and curly braces without parentheses.

2. Step 2: Check each option

   actor DataManager { } uses correct syntax: actor DataManager { }. actor DataManager() { } incorrectly adds parentheses after the name.

3. Final Answer:

   actor DataManager { } -> Option B

4. Quick Check:

   Correct actor syntax = actor Name { } [OK]

Hint: Actors do not use parentheses after their name [OK]

Common Mistakes:

• Adding parentheses after actor name
• Using class or struct instead of actor
• Omitting curly braces

3. What will be the output of the following Swift code?

actor Counter {
    var value = 0
    func increment() {
        value += 1
    }
}

let counter = Counter()
Task {
    await counter.increment()
    print(await counter.value)
}

medium

A. 1

B. 0

C. Compilation error

D. Runtime error

Solution

1. Step 1: Understand actor behavior and method calls

   The actor Counter has a variable value initialized to 0 and a method increment() that adds 1 to value. The method is called with await inside a Task.

2. Step 2: Trace the code execution

   The increment() method increases value from 0 to 1. Then print(await counter.value) prints the updated value, which is 1.

3. Final Answer:

   1 -> Option A

4. Quick Check:

   Incremented value = 1 [OK]

Hint: Remember to await actor method calls and property access [OK]

Common Mistakes:

• Forgetting to use await with actor calls
• Expecting initial value 0 after increment
• Assuming synchronous access to actor properties

4. Identify the error in the following actor declaration and fix it:

actor Logger {
    var logs: [String]
    func addLog(_ message: String) {
        logs.append(message)
    }
}

medium

A. Missing initialization of 'logs' array

B. Actor cannot have functions

C. Use 'class' instead of 'actor'

D. Missing 'await' keyword in function

Solution

1. Step 1: Check property initialization in actor

   The property logs is declared but not initialized. In Swift, stored properties must have initial values or be initialized in an initializer.

2. Step 2: Identify the fix

   Initialize logs as an empty array: var logs: [String] = [] to fix the error.

3. Final Answer:

   Missing initialization of 'logs' array -> Option A

4. Quick Check:

   Stored properties need initial values [OK]

Hint: Always initialize stored properties in actors [OK]

Common Mistakes:

• Assuming default initialization for arrays
• Thinking actors cannot have functions
• Forgetting to add await when calling actor methods

5. You want to create an actor BankAccount that safely manages a balance. Which of the following code snippets correctly declares the actor and provides a method to deposit money asynchronously?

hard

A. actor BankAccount {
var balance: Double = 0.0
func deposit(amount: Double) {
balance += amount
}
}

B. actor BankAccount {
var balance: Double = 0.0
func deposit(amount: Double) {
await balance += amount
}
}

C. actor BankAccount {
var balance: Double = 0.0
func deposit(amount: Double) async {
await Task.sleep(1_000_000_000)
balance += amount
}
}

D. class BankAccount {
var balance: Double = 0.0
func deposit(amount: Double) async {
balance += amount
}
}

Solution

1. Step 1: Understand actor method concurrency

   Actor methods that perform asynchronous work should be marked async. actor BankAccount { var balance: Double = 0.0 func deposit(amount: Double) { balance += amount } } lacks async on the method, so it cannot await inside.

2. Step 2: Check for realistic async behavior

   actor BankAccount { var balance: Double = 0.0 func deposit(amount: Double) async { await Task.sleep(1_000_000_000) balance += amount } } marks deposit as async and simulates asynchronous delay with await Task.sleep(), showing proper async usage inside an actor.

3. Step 3: Verify actor declaration

   class BankAccount { var balance: Double = 0.0 func deposit(amount: Double) async { balance += amount } } uses class instead of actor, so it does not provide concurrency safety.

4. Final Answer:

   correctly declares an actor with an async deposit method including await -> Option C

5. Quick Check:

   Actor + async method + await inside = actor BankAccount { var balance: Double = 0.0 func deposit(amount: Double) async { await Task.sleep(1_000_000_000) balance += amount } } [OK]

Hint: Async actor methods must be marked async and use await inside [OK]

Common Mistakes:

• Omitting async keyword on async actor methods
• Using class instead of actor for concurrency
• Not using await inside async methods when needed