Unit type as void equivalent in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin function returning Unit?

Consider the following Kotlin code. What will be printed when printResult() is called?

Kotlin

fun printResult(): Unit {
    println("Hello from Unit function")
}

fun main() {
    printResult()
}

A Hello from Unit function

B null

C Unit

D No output

💡 Hint

Remember that Unit functions can print output but do not return a value to print.

The function prints the string inside it. Since it returns Unit, the return value is not printed, only the println output appears.

❓ Predict Output

intermediate

What is the value of variable x after this Unit function call?

Look at this Kotlin code. What is the value of x after calling val x = printMessage()?

Kotlin

fun printMessage(): Unit {
    println("Message printed")
}

fun main() {
    val x = printMessage()
    println(x)
}

A Compilation error

B null

C Message printed

D Unit

💡 Hint

Functions returning Unit assign Unit to variables.

In Kotlin, functions returning Unit assign the singleton Unit object to variables. So x is Unit, which prints as "kotlin.Unit".

🔧 Debug

advanced

Why does this Kotlin code cause a compilation error?

Examine the code below. Why does it fail to compile?

Kotlin

fun doSomething(): Unit {
    return 5
}

fun main() {
    doSomething()
}

A Cannot return a value from a function with Unit return type

B Unit functions must return null explicitly

C Missing return statement

D The function must return a String

💡 Hint

Unit means no meaningful value is returned.

Functions declared with return type Unit cannot return any value. Returning 5 causes a type mismatch error.

🧠 Conceptual

advanced

Which statement about Kotlin's Unit type is true?

Choose the correct statement about the Unit type in Kotlin.

A Unit functions must always return null explicitly

B Unit is equivalent to Java's null

C Unit is a singleton object representing no meaningful value

D Unit is a primitive type like Int or Boolean

💡 Hint

Think about what Unit represents in Kotlin functions.

Unit is a singleton object used to indicate a function returns no meaningful value, similar to void in Java but it is an actual type.

❓ Predict Output

expert

What is the output of this Kotlin code involving Unit?

Analyze the code and select the exact output printed to the console.

Kotlin

fun foo(): Unit {
    println("Start")
    return Unit
}

fun main() {
    val result = foo()
    println(result)
}

A Start

B

Start
kotlin.Unit

C

Start
Unit

D

Start
null

💡 Hint

The function prints "Start" and returns Unit which prints as kotlin.Unit.

The function prints "Start" first. The variable result holds Unit, which prints as "kotlin.Unit".