Suspend functions concept in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a suspend function named fetchData.

Kotlin

suspend fun [1]() {
    // simulate fetching data
}

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

AfetchData

BretrieveData

CloadData

DgetData

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name than requested.

The function name must be fetchData as requested.

2fill in blank

medium

Complete the code to call the suspend function fetchData inside a coroutine scope.

Kotlin

import kotlinx.coroutines.*

fun main() = runBlocking {
    [1]()
}

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Alaunch

Basync

CfetchData

Ddelay

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to launch or async instead of calling the function directly.

You need to call the suspend function fetchData() inside runBlocking.

3fill in blank

hard

Fix the error in the suspend function declaration by filling the blank.

Kotlin

fun [1] fetchData() {
    // code
}

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

Asuspend

Basync

Claunch

Dcoroutine

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'async' or 'launch' as function modifiers instead of 'suspend'.

The keyword suspend is required before the function name to declare a suspend function.

4fill in blank

hard

Fill both blanks to create a suspend function that delays for 1000 milliseconds and then prints a message.

Kotlin

suspend fun waitAndPrint() {
    [1](1000L)
    println([2])
}

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Adelay

B"Done waiting!"

C"Waiting finished"

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'print' instead of 'println', or wrong string message.

The delay function pauses the coroutine, and then the message "Done waiting!" is printed.

5fill in blank

hard

Fill all three blanks to create a suspend function that fetches data, delays, and returns a string result.

Kotlin

suspend fun fetchData(): String {
    val data = "Data"
    [1](500L)
    return [2] + [3]
}

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

Adelay

Bdata

C" fetched"

D"done"

Attempts:

3 left

💡 Hint

Common Mistakes

Returning wrong strings or forgetting to delay.

The function delays for 500 milliseconds, then returns the string data + " fetched".

Practice

1. What is the main purpose of a suspend function in Kotlin?

easy

A. To mark the function as deprecated

B. To make the function run faster by using multiple threads

C. To allow the function to pause and resume without blocking the thread

D. To convert the function into a lambda expression

Solution

1. Step 1: Understand what suspend functions do

   Suspend functions let the program pause execution at some point and resume later without blocking the thread.

2. Step 2: Compare options with this behavior

   Only To allow the function to pause and resume without blocking the thread describes this pausing and resuming behavior correctly.

3. Final Answer:

   To allow the function to pause and resume without blocking the thread -> Option C

4. Quick Check:

   Suspend function purpose = pause and resume without blocking [OK]

Hint: Suspend means pause and resume without blocking [OK]

Common Mistakes:

• Thinking suspend means multithreading
• Confusing suspend with deprecated functions
• Assuming suspend converts functions to lambdas

2. Which of the following is the correct way to declare a suspend function in Kotlin?

easy

A. fun suspend fetchData() { }

B. fun fetchData() suspend { }

C. suspend fetchData fun() { }

D. suspend fun fetchData() { }

Solution

1. Step 1: Recall suspend function syntax

   The correct syntax places the suspend keyword before fun.

2. Step 2: Check each option

   Only suspend fun fetchData() { } matches the correct syntax: suspend fun fetchData() { }.

3. Final Answer:

   suspend fun fetchData() { } -> Option D

4. Quick Check:

   Suspend function syntax = suspend before fun [OK]

Hint: Remember: suspend keyword comes before fun [OK]

Common Mistakes:

• Placing suspend after fun
• Putting suspend after function name
• Mixing order of keywords

3. What will be the output of the following Kotlin code?

import kotlinx.coroutines.*
suspend fun greet() {
    delay(100)
    println("Hello from suspend")
}
fun main() = runBlocking {
    greet()
    println("Done")
}

medium

A. Hello from suspend\nDone

B. Done\nHello from suspend

C. Compilation error because greet() is suspend

D. Runtime error because delay() is not allowed here

Solution

1. Step 1: Understand runBlocking and suspend call

   runBlocking starts a coroutine and allows calling suspend functions like greet().

2. Step 2: Trace execution order

   greet() delays 100ms, then prints "Hello from suspend". After greet() finishes, main prints "Done".

3. Final Answer:

   Hello from suspend\nDone -> Option A

4. Quick Check:

   Output order = greet() then Done [OK]

Hint: runBlocking lets you call suspend functions directly [OK]

Common Mistakes:

• Assuming greet() runs asynchronously and prints after Done
• Thinking delay causes errors outside coroutine
• Confusing suspend function calls outside coroutines

4. Identify the error in this Kotlin code snippet:

fun fetchData() {
    delay(1000)
    println("Data fetched")
}

medium

A. delay() cannot be called from a non-suspend function

B. println() is not allowed inside functions

C. fetchData() must return a value

D. delay() requires an integer argument, 1000 is invalid

Solution

1. Step 1: Check usage of delay()

   delay() is a suspend function and can only be called from suspend functions or coroutines.

2. Step 2: Analyze fetchData() declaration

   fetchData() is a regular function without suspend keyword, so calling delay() inside causes an error.

3. Final Answer:

   delay() cannot be called from a non-suspend function -> Option A

4. Quick Check:

   delay() call requires suspend function context [OK]

Hint: delay() only works inside suspend functions [OK]

Common Mistakes:

• Thinking delay() works in normal functions
• Believing println() is restricted
• Confusing delay() argument type

5. You want to write a suspend function fetchUserData() that calls another suspend function fetchFromNetwork() and returns its result. Which of the following is the correct way to implement fetchUserData()?

hard

A. fun fetchUserData() = fetchFromNetwork()

B. suspend fun fetchUserData() = fetchFromNetwork()

C. fun suspend fetchUserData() = fetchFromNetwork()

D. suspend fun fetchUserData() { fetchFromNetwork() }

Solution

1. Step 1: Recognize suspend function chaining rules

   A suspend function calling another suspend function must itself be marked suspend.

2. Step 2: Check each option's syntax and behavior

   suspend fun fetchUserData() = fetchFromNetwork() correctly declares fetchUserData() as suspend and returns fetchFromNetwork() result. The option with suspend fun fetchUserData() { fetchFromNetwork() } misses returning the result. The remaining options have incorrect syntax.

3. Final Answer:

   suspend fun fetchUserData() = fetchFromNetwork() -> Option B

4. Quick Check:

   Calling suspend inside suspend requires suspend keyword [OK]

Hint: Suspend functions calling suspend must also be suspend [OK]

Common Mistakes:

• Omitting suspend keyword on calling function
• Using wrong suspend syntax order
• Not returning the result from called suspend function