Single-expression functions in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a single-expression function in Kotlin?

A single-expression function is a function that returns the result of a single expression directly without using curly braces or the return keyword.

beginner

How do you write a single-expression function that adds two numbers in Kotlin?

fun add(a: Int, b: Int) = a + b

intermediate

Can single-expression functions have explicit return types in Kotlin?

Yes, you can specify the return type explicitly, but Kotlin can often infer it automatically.

beginner

What is the benefit of using single-expression functions?

They make the code shorter, cleaner, and easier to read by removing unnecessary syntax like braces and return statements.

beginner

Is this a valid single-expression function in Kotlin? <br>

fun greet() = println("Hello")

Yes, it is valid. The function calls println as a single expression and returns Unit.

Which of the following is a correct single-expression function in Kotlin?

A fun square(x: Int): Int { x * x }

B fun square(x: Int) { return x * x }

C fun square(x: Int) { x * x }

D fun square(x: Int) = x * x

Option D uses the single-expression syntax with '=' and no braces, which is correct.

What is the return type of this function? <br>

fun isEven(n: Int) = n % 2 == 0

A Boolean

B Int

C Unit

D String

The expression 'n % 2 == 0' returns a Boolean value.

Can a single-expression function have multiple statements inside it?

A No, it can only have one expression.

B Only if wrapped in curly braces.

C Yes, but only if separated by semicolons.

D Yes, it can have any number of statements.

Single-expression functions can only have one expression, no multiple statements.

Which keyword is NOT needed in a single-expression function?

A fun

B return

C =

D parameter types

The 'return' keyword is not needed because the expression result is returned automatically.

What does this function return? <br>

fun greet() = println("Hi")

A String "Hi"

B Nothing

C Unit

D Boolean

println returns Unit, so the function returns Unit.

Explain what a single-expression function is and how it differs from a regular function in Kotlin.

Think about how the function body is written and how the result is returned.

Write a single-expression function in Kotlin that checks if a number is positive.

Use a comparison expression like 'n > 0'.