Await keyword in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to wait for the asynchronous function to finish before printing the result.

iOS Swift

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

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

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

Atry

Basync

Cdefer

Dawait

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'async' instead of 'await' before the function call.

Omitting the keyword and calling the function directly.

The await keyword pauses the function until the asynchronous call completes, then returns the result.

2fill in blank

medium

Complete the code to mark the function as asynchronous so it can use 'await'.

iOS Swift

func fetchUser() [1] -> String {
    return "User data"
}

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

Aawait

Bsync

Casync

Dthrows

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'await' to mark the function instead of 'async'.

Forgetting to mark the function as async when using await inside.

The async keyword marks a function as asynchronous, allowing it to use await inside.

3fill in blank

hard

Fix the error in calling an async function inside an asynchronous function by adding the missing keyword.

iOS Swift

func syncFunction() async {
    let data = [1] fetchData()
    print(data)
}

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

Aawait

Bdefer

Ctry

Dasync

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the async function without 'await', causing errors.

Using 'async' instead of 'await' before the call.

You must use await to call an async function and wait for its result.

4fill in blank

hard

Fill both blanks to correctly define and call an async function that returns a string.

iOS Swift

func getMessage() [1] -> String {
    return "Hello"
}

func show() async {
    let message = [2] getMessage()
    print(message)
}

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

Aasync

Bawait

Cthrows

Ddefer

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to mark the function as async.

Calling the async function without await.

The function must be marked async to be asynchronous, and the call must use await to wait for its result.

5fill in blank

hard

Fill all three blanks to create an async function, call it with await, and handle errors with try.

iOS Swift

func fetchInfo() [1] throws -> String {
    return "Info"
}

func process() async {
    do {
        let info = [2] [3] fetchInfo()
        print(info)
    } catch {
        print("Error")
    }
}

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

Aasync

Bawait

Ctry

Ddefer

Attempts:

3 left

💡 Hint

Common Mistakes

Using try without await or vice versa.

Not marking the function as async when it uses await.

The function is marked async and throws. When calling it, use try and await to handle errors and wait for the result.

Practice

1. What does the await keyword do in Swift's async functions?

easy

A. It converts a synchronous function to asynchronous.

B. It makes the function run faster.

C. It pauses the function until the async task completes.

D. It cancels the async task immediately.

Solution

1. Step 1: Understand the role of await

   The await keyword pauses the execution of an async function until the awaited task finishes.

2. Step 2: Compare other options

   Options B, C, and D describe behaviors that await does not perform.

3. Final Answer:

   It pauses the function until the async task completes. -> Option C

4. Quick Check:

   await pauses async tasks = A [OK]

Hint: Remember: await waits for task completion before continuing [OK]

Common Mistakes:

• Thinking await speeds up the function
• Using await outside async functions
• Confusing await with task cancellation

2. Which of the following is the correct way to declare an async function that uses await inside it?

easy

A. func fetchData() async { let data = await loadData() }

B. func fetchData() { let data = await loadData() }

C. async func fetchData() { let data = await loadData() }

D. func fetchData() async await { let data = loadData() }

Solution

1. Step 1: Check async function declaration syntax

   In Swift, the correct syntax is func name() async {} to declare an async function.

2. Step 2: Verify usage of await inside async function

   func fetchData() async { let data = await loadData() } correctly uses await inside an async function. Options B, C, and D have syntax errors.

3. Final Answer:

   func fetchData() async { let data = await loadData() } -> Option A

4. Quick Check:

   Async function syntax = A [OK]

Hint: Async functions must have 'async' keyword before braces [OK]

Common Mistakes:

• Omitting async keyword in function declaration
• Placing async before func keyword
• Adding await in function signature

3. What will be printed by this Swift code?

func fetchNumber() async -> Int {
  return 5
}

func printNumber() async {
  let number = await fetchNumber()
  print(number)
}

Task {
  await printNumber()
}

medium

A. No output, code has syntax error

B. 5

C. 0

D. The program crashes

Solution

1. Step 1: Understand async function behavior

   The function fetchNumber() returns 5 asynchronously. Using await waits for this result.

2. Step 2: Trace the print statement

   The printNumber() function awaits fetchNumber() and prints the returned value 5.

3. Final Answer:

   5 -> Option B

4. Quick Check:

   Await returns value before print = C [OK]

Hint: Await pauses until value returns, then prints it [OK]

Common Mistakes:

• Expecting 0 because of async
• Thinking code crashes without main thread
• Confusing async function call without await

4. Identify the error in this Swift code snippet:

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

func showData() {
  let result = await loadData()
  print(result)
}

medium

A. Missing async keyword in showData function declaration.

B. print statement is not allowed inside async functions.

C. loadData function should not return String.

D. Cannot use await inside a non-async function.

Solution

1. Step 1: Check function declarations and await usage

   The function showData() is not marked async but uses await, which is invalid.

2. Step 2: Understand await usage rules

   In Swift, await can only be used inside async functions. So showData() must be async to use await.

3. Final Answer:

   Cannot use await inside a non-async function. -> Option D

4. Quick Check:

   Await only in async functions = D [OK]

Hint: Await requires async function context [OK]

Common Mistakes:

• Forgetting to mark function async when using await
• Thinking await works in normal functions
• Misunderstanding return types with async

5. You want to fetch user data and then fetch user posts, both are async functions. Which code correctly waits for both tasks in order using await?

hard

A. func loadUserData() async {
let user = await fetchUser()
let posts = await fetchPosts(user.id)
print(posts)
}

B. func loadUserData() async {
let user = fetchUser()
let posts = fetchPosts(user.id)
print(posts)
}

C. func loadUserData() {
let user = await fetchUser()
let posts = await fetchPosts(user.id)
print(posts)
}

D. func loadUserData() async {
let user = await fetchUser()
let posts = fetchPosts(user.id)
print(posts)
}

Solution

1. Step 1: Confirm async function declaration

   The function must be marked async to use await inside it, so options A and D are candidates.

2. Step 2: Check await usage for both async calls

   func loadUserData() async { let user = await fetchUser() let posts = await fetchPosts(user.id) print(posts) } awaits both fetchUser() and fetchPosts(), ensuring sequential completion. func loadUserData() async { let user = await fetchUser() let posts = fetchPosts(user.id) print(posts) } misses await on fetchPosts().

3. Final Answer:

   func loadUserData() async { let user = await fetchUser() let posts = await fetchPosts(user.id) print(posts) } -> Option A

4. Quick Check:

   Await both async calls in async function = B [OK]

Hint: Await each async call to run in order inside async function [OK]

Common Mistakes:

• Forgetting await on second async call
• Not marking function async
• Calling async functions without await