Structured concurrency model in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a new asynchronous task using Swift's structured concurrency.

Swift

Task.[1] {
    print("Hello from a new task!")
}

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

Adetached

Binit

Cstart

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using Task.start or Task.run which do not exist.

Confusing Task.detached with Task.init.

In Swift's structured concurrency, you create a new detached task using Task.detached { ... }.

2fill in blank

medium

Complete the code to await the result of an asynchronous function call.

Swift

func fetchData() async -> String {
    return "Data"
}

func process() async {
    let result = [1] fetchData()
    print(result)
}

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

Aawait

Bcall

Casync

Ddefer

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use 'await' before calling an async function.

Using 'async' instead of 'await' in the function body.

The 'await' keyword is used to wait for an asynchronous function to complete and return its result.

3fill in blank

hard

Fix the error in the code by completing the blank to correctly create a child task within a task group.

Swift

func downloadAll() async {
    await withTaskGroup(of: String.self) { group in
        group.[1] {
            return "File 1"
        }
    }
}

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

AstartTask

BcreateTask

Claunch

DaddTask

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like startTask or createTask.

Trying to use Task.detached inside the group.

In Swift's structured concurrency, you add child tasks to a task group using group.addTask { ... }.

4fill in blank

hard

Fill both blanks to create a task group that collects results from multiple child tasks.

Swift

func fetchAll() async {
    let results = await withTaskGroup(of: String.self) { group in
        group.[1] {
            return "Data 1"
        }
        group.[2] {
            return "Data 2"
        }
    }
}

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

AaddTask

Bstart

Claunch

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using different methods for each task.

Using methods that do not exist on the group.

You add multiple child tasks to a task group using group.addTask { ... } for each task.

5fill in blank

hard

Fill all three blanks to create a task group that adds tasks and processes their results.

Swift

func processFiles() async {
    await withTaskGroup(of: String.self) { group in
        group.[1] {
            return "File A"
        }
        group.[2] {
            return "File B"
        }
        for await result in group.[3] {
            print(result)
        }
    }
}

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

AaddTask

BstartTask

Cresults

Dtasks

Attempts:

3 left

💡 Hint

Common Mistakes

Using startTask instead of addTask.

Trying to iterate over group.tasks instead of group.results.

You add tasks with addTask and iterate over the group's results property to get completed task results.

Practice

1. What is the main purpose of structured concurrency in Swift?

easy

A. To group tasks so they run safely and complete before continuing

B. To allow tasks to run forever without waiting

C. To make tasks run only on the main thread

D. To avoid using async and await keywords

Solution

1. Step 1: Understand structured concurrency concept

   Structured concurrency groups related tasks so they run safely and finish before the program moves on.

2. Step 2: Compare options with concept

   Only To group tasks so they run safely and complete before continuing correctly describes grouping tasks to run safely and complete before continuing.

3. Final Answer:

   To group tasks so they run safely and complete before continuing -> Option A

4. Quick Check:

   Structured concurrency = safe grouped tasks [OK]

Hint: Structured concurrency means tasks finish before moving on [OK]

Common Mistakes:

• Thinking tasks run forever without waiting
• Believing tasks only run on main thread
• Confusing structured concurrency with avoiding async/await

2. Which of the following is the correct syntax to create a task group in Swift?

easy

A. withTaskGroup(of: Int.self) { group in ... }

B. asyncGroup { ... }

C. taskGroup.run { ... }

D. TaskGroup { await ... }

Solution

1. Step 1: Recall correct task group syntax

   Swift uses withTaskGroup(of: Type.self) { group in ... } to create a task group.

2. Step 2: Check options for exact syntax

   Only withTaskGroup(of: Int.self) { group in ... } matches the correct syntax; others are invalid or made-up.

3. Final Answer:

   withTaskGroup(of: Int.self) { group in ... } -> Option A

4. Quick Check:

   Task group syntax = withTaskGroup(of:) [OK]

Hint: Task groups start with withTaskGroup(of:) [OK]

Common Mistakes:

• Using TaskGroup without 'with'
• Trying taskGroup.run which doesn't exist
• Using asyncGroup which is not a Swift keyword

3. What will be the output of this Swift code using a task group?

func fetchValues() async -> [Int] {
  await withTaskGroup(of: Int.self) { group in
    group.addTask { 3 }
    group.addTask { 7 }
    group.addTask { 2 }

    var results = [Int]()
    for await value in group {
      results.append(value)
    }
    return results.sorted()
  }
}

Task {
  let values = await fetchValues()
  print(values)
}

medium

A. [3, 7, 2]

B. [2, 3, 7]

C. [7, 3, 2]

D. Compilation error

Solution

1. Step 1: Understand task group execution

   The tasks return 3, 7, and 2 asynchronously. The for-await loop collects them in any order.

2. Step 2: Analyze the return statement

   The results array is sorted before returning, so output is sorted ascending: [2, 3, 7].

3. Final Answer:

   [2, 3, 7] -> Option B

4. Quick Check:

   Sorted results = [2, 3, 7] [OK]

Hint: Remember results are sorted before printing [OK]

Common Mistakes:

• Assuming tasks run in order added
• Forgetting the sorting step
• Thinking code causes compile error

4. Identify the error in this Swift code using a task group:

func calculateSum() async -> Int {
  await withTaskGroup(of: Int.self) { group in
    group.addTask { 10 }
    group.addTask { 20 }
    var total = 0
    for value in group {
      total += value
    }
    return total
  }
}

medium

A. Return type should be Void

B. Cannot add tasks inside withTaskGroup

C. Missing 'await' before 'for' loop

D. Variable 'total' should be declared outside the group

Solution

1. Step 1: Check for correct async iteration

   When iterating over a task group, 'for await' must be used to await each task's result.

2. Step 2: Identify missing 'await'

   The code uses 'for value in group' instead of 'for await value in group', causing a syntax error.

3. Final Answer:

   Missing 'await' before 'for' loop -> Option C

4. Quick Check:

   Async iteration requires 'for await' [OK]

Hint: Use 'for await' to loop over task groups [OK]

Common Mistakes:

• Using 'for' instead of 'for await' on task groups
• Thinking tasks can't be added inside withTaskGroup
• Misunderstanding return type requirements

5. You want to fetch user data and user posts concurrently using structured concurrency. Which approach correctly uses a task group to run both tasks and combine their results?

hard

A. Use DispatchQueue.global().async to run tasks and wait with sleep()

B. Run tasks sequentially without a task group to avoid concurrency issues

C. Create two separate Task blocks and return results without waiting

D. Use withTaskGroup to add two tasks fetching data and posts, then await all and return combined tuple

Solution

1. Step 1: Understand concurrency for multiple async tasks

   Structured concurrency uses task groups to run multiple async tasks concurrently and wait for all to finish.

2. Step 2: Evaluate options for correct concurrency usage

   Use withTaskGroup to add two tasks fetching data and posts, then await all and return combined tuple correctly uses withTaskGroup to add tasks, await their completion, and combine results safely.

3. Final Answer:

   Use withTaskGroup to add two tasks fetching data and posts, then await all and return combined tuple -> Option D

4. Quick Check:

   Task groups run and wait for multiple tasks [OK]

Hint: Use withTaskGroup to run and wait multiple tasks [OK]

Common Mistakes:

• Running tasks sequentially losing concurrency benefits
• Using DispatchQueue with sleep instead of structured concurrency
• Not waiting for tasks to finish before returning