Why async/await simplifies concurrent code in iOS Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an asynchronous function in Swift.

iOS Swift

func fetchData() [1] {
  // code to fetch data
}

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

Aasync

Bawait

Cthrows

Dsync

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using 'throws' which is for error handling, not async behavior.

In Swift, you declare an asynchronous function by adding the async keyword after the function signature.

2fill in blank

medium

Complete the code to call an asynchronous function using await.

iOS Swift

func load() async {
  let data = try? [1] fetchData()
}

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

Aawait

Basync

Casync await

Dtry

Attempts:

3 left

💡 Hint

Common Mistakes

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

Omitting the 'await' keyword causing compile errors.

To call an asynchronous function and wait for its result, use the await keyword before the function call.

3fill in blank

hard

Fix the error in the code by adding the missing keyword to handle asynchronous code.

iOS Swift

func process() [1] {
  let result = try? await fetchData()
}

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

Async

Bawait

Cthrows

Dasync

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to mark the function as async causes compile errors.

Trying to use await inside a synchronous function.

The function calling await must itself be marked async to handle asynchronous code properly.

4fill in blank

hard

Fill both blanks to create a task that runs asynchronous code concurrently.

iOS Swift

Task.[1] {
  let data = try? [2] fetchData()
}

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

Adetached

Bawait

Casync

Dsync

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'async' instead of 'await' inside the task.

Not using 'detached' to create a concurrent task.

Use Task.detached to start a new concurrent task, and await to wait for the async function inside it.

5fill in blank

hard

Fill all three blanks to define an async function that returns a string after awaiting another async call.

iOS Swift

func getMessage() [1] [2] -> String {
  let data = try? [3] fetchData()
  return data ?? "No data"
}

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

Aasync

Bawait

Cthrows

Dsync

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to mark the function as async and throws.

Not using await before the async function call.

The function is marked async and throws because it can throw errors. Inside, await is used to wait for the async call.

Practice

1. What is the main benefit of using async/await in Swift for concurrent tasks?

easy

A. It replaces all synchronous code with asynchronous code.

B. It automatically speeds up the app without any code changes.

C. It prevents any errors from happening in the code.

D. It makes asynchronous code easier to read and write.

Solution

1. Step 1: Understand async/await purpose

   Async/await helps write asynchronous code that looks like normal, simple code.

2. Step 2: Compare benefits

   It does not automatically speed up or replace all code, nor prevent all errors, but it improves readability and flow.

3. Final Answer:

   It makes asynchronous code easier to read and write. -> Option D

4. Quick Check:

   Async/await improves code readability = C [OK]

Hint: Async/await makes async code look like normal code [OK]

Common Mistakes:

• Thinking async/await automatically speeds up code
• Believing async/await removes all errors
• Confusing async/await with synchronous code

2. Which of the following is the correct syntax to declare an asynchronous function in Swift?

easy

A. async func fetchData() throws -> String

B. func fetchData() async throws -> String

C. func async fetchData() throws -> String

D. func fetchData() throws async -> String

Solution

1. Step 1: Recall async function syntax

   In Swift, the async keyword comes after the function parentheses.

2. Step 2: Check option syntax

   func fetchData() async throws -> String correctly places async after parentheses and before throws.

3. Final Answer:

   func fetchData() async throws -> String -> Option B

4. Quick Check:

   Async keyword after parentheses = A [OK]

Hint: Remember async goes right after function parentheses [OK]

Common Mistakes:

• Placing async before func keyword
• Putting async after throws keyword
• Mixing order of async and throws

3. What will be printed by this Swift code using async/await?

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

Task {
  let number = await fetchNumber()
  print(number)
}

medium

A. 5

B. Optional(5)

C. Task

D. No output

Solution

1. Step 1: Understand async function return

   The function fetchNumber() returns an Int value 5 asynchronously.

2. Step 2: Await and print result

   The await keyword waits for the result, then print(number) outputs 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Await fetch returns 5 printed = D [OK]

Hint: Await unwraps async result before printing [OK]

Common Mistakes:

• Expecting Optional(5) instead of 5
• Thinking Task prints itself
• Assuming no output without await

4. Identify the error in this Swift async/await code:

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

let result = await loadData()
print(result)

medium

A. Cannot use await outside an async context

B. Missing return type in function

C. Function should not be async

D. Await keyword is misspelled

Solution

1. Step 1: Check await usage context

   In Swift, await must be called inside an async function or async context.

2. Step 2: Analyze code structure

   The code calls await loadData() at top-level, which is not allowed.

3. Final Answer:

   Cannot use await outside an async context -> Option A

4. Quick Check:

   Await requires async context = A [OK]

Hint: Await only works inside async functions [OK]

Common Mistakes:

• Calling await in synchronous code
• Ignoring async context requirement
• Assuming await works anywhere

5. You want to fetch user info and user posts concurrently using async/await in Swift. Which code correctly runs both tasks at the same time and waits for both results?

hard

A. let user = await fetchUser()
let posts = await fetchPosts()

B. fetchUser()
fetchPosts()
print("Done")

C. async let user = fetchUser()
async let posts = fetchPosts()
let userInfo = await user
let userPosts = await posts

D. Task {
let user = fetchUser()
let posts = fetchPosts()
print(user, posts)
}

Solution

1. Step 1: Understand concurrent async calls

   Using async let starts tasks concurrently without waiting immediately.

2. Step 2: Await both results

   Awaiting user and posts later waits for both to finish, running in parallel.

3. Final Answer:

   async let user = fetchUser() async let posts = fetchPosts() let userInfo = await user let userPosts = await posts -> Option C

4. Quick Check:

   async let runs tasks concurrently = B [OK]

Hint: Use async let to run tasks in parallel [OK]

Common Mistakes:

• Awaiting tasks one after another (sequential)
• Not awaiting async let variables
• Calling async functions without await