Distributed actors overview in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple distributed actor method call

What is the output of this Swift code using a distributed actor?

Swift

distributed actor Counter {
    var value = 0
    distributed func increment() async {
        value += 1
    }
    func current() -> Int {
        return value
    }
}

func test() async {
    let counter = Counter()
    await counter.increment()
    print(counter.current())
}

task {
    await test()
}

A 1

B Runtime error

C Compilation error

D 0

💡 Hint

Remember that distributed functions are asynchronous and may not update local state immediately.

The distributed func increment() is asynchronous and runs remotely, so the local value is not updated immediately. The current() method returns the local value, which remains 0.

🧠 Conceptual

intermediate

Understanding the role of distributed actor identity

What is the main purpose of the identity property in a distributed actor?

A To store the actor's internal state

B To uniquely identify the actor instance across the network

C To define the actor's concurrency model

D To manage local memory allocation

💡 Hint

Think about how distributed actors communicate remotely.

The identity property uniquely identifies a distributed actor instance across the network, allowing remote calls to be routed correctly.

🔧 Debug

advanced

Identify the error in distributed actor initialization

What error will this code produce and why?

Swift

distributed actor Logger {
    let id: UUID
    init() {
        id = UUID()
    }
}

func test() {
    let logger = Logger()
}

A No error, code runs fine

B Runtime error: missing actor system

C Compilation error: distributed actors require a distributed actor system parameter in init

D Compilation error: distributed actors cannot have stored properties

💡 Hint

Distributed actors need a system to manage their identity and communication.

Distributed actors require an actor system parameter in their initializer to manage identity and remote communication. The code lacks this parameter, causing a compilation error.

📝 Syntax

advanced

Correct syntax for distributed function declaration

Which option correctly declares a distributed function in a distributed actor?

Swift

distributed actor Service {
    ???
}

A distributed func fetchData() async throws -> String

B func distributed fetchData() async throws -> String

C distributed func fetchData() -> String

D func fetchData() distributed async throws -> String

💡 Hint

The 'distributed' keyword comes before 'func'.

The correct syntax places 'distributed' before 'func' and supports async and throws modifiers.

🚀 Application

expert

Predict the number of items in a distributed actor's dictionary after remote calls

Given this distributed actor code, how many key-value pairs will the dictionary contain after the calls?

Swift

distributed actor Store {
    var items: [String: Int] = [:]
    distributed func addItem(key: String, value: Int) async {
        items[key] = value
    }
    func countItems() -> Int {
        return items.count
    }
}

func test() async {
    let store = Store()
    await store.addItem(key: "a", value: 1)
    await store.addItem(key: "b", value: 2)
    print(store.countItems())
}

task {
    await test()
}

A 0

B 1

C Compilation error

D 2

💡 Hint

Distributed functions run remotely and do not update local state immediately.

The distributed func addItem runs remotely and updates the remote state, but the local 'items' dictionary remains empty. The countItems() method returns the local count, which is 0.