Actors vs locks decision in Swift - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an actor in Swift.

Swift

actor [1] {
    var count = 0
}

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Aenum

Bclass

Cstruct

DCounter

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' or 'struct' instead of an actor name.

In Swift, actor is followed by the actor's name, like Counter.

2fill in blank

medium

Complete the code to call an async method on an actor instance.

Swift

let counter = Counter()
Task {
    await counter.[1]()
}

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Aincrement

BincrementSync

CincrementNow

DincrementLater

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that imply synchronous calls which are not allowed on actors.

Actor methods that modify state are usually async, so calling increment() with await is correct.

3fill in blank

hard

Fix the error in the code to safely access shared data using a lock.

Swift

class SafeCounter {
    private var count = 0
    private let lock = NSLock()

    func increment() {
        [1].lock()
        count += 1
        lock.unlock()
    }
}

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Acounter

Block

Cself

DNSLock

Attempts:

3 left

💡 Hint

Common Mistakes

Calling lock() on 'self' or class name instead of the lock instance.

The lock instance must be used to call lock() and unlock() to protect the critical section.

4fill in blank

hard

Fill in the blank to create a dictionary filter that selects keys with values greater than 10.

Swift

let filtered = dictionary.filter { $0.value [1] 10 }.map { ($0.key, $0.value) }
let result = Dictionary(uniqueKeysWithValues: filtered) // Result dictionary

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A!=

B<

C>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '==' which filter wrong values.

To filter values greater than 10, use the '>' operator in the filter closure.

5fill in blank

hard

Fill all three blanks to create an actor method that safely increments and returns the count.

Swift

actor Counter {
    private var count = 0

    func incrementAndGet() async -> Int {
        [1]
        count += 1
        let current = [2]
        [3]
        return current
    }
}

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Aawait Task.sleep(nanoseconds: 0)

Bcount

Cawait Task.yield()

Dcount + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Returning wrong values or missing async suspension points.

Using await Task.sleep(nanoseconds: 0) and await Task.yield() simulates async suspension points. The count variable holds the current value after increment.