Lambda syntax and declaration in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a lambda expression in Kotlin?

A lambda expression is a small block of code that can be passed around and executed later. It is like a mini-function without a name.

beginner

How do you declare a simple lambda that takes two integers and returns their sum?

You write: { a: Int, b: Int -> a + b }. This means the lambda takes two integers a and b and returns their sum.

beginner

What is the syntax to assign a lambda to a variable in Kotlin?

You assign it like this: val sum: (Int, Int) -> Int = { a, b -> a + b }. Now sum holds the lambda and you can call it like a function.

beginner

How do you call a lambda stored in a variable?

If you have val greet = { name: String -> "Hello, $name!" }, you call it like this: greet("Alice").

intermediate

What is the implicit name for a single parameter in a Kotlin lambda?

If a lambda has only one parameter, you can use it instead of naming it explicitly. For example: { it * 2 } doubles the input.

Which of the following is a correct Kotlin lambda syntax for adding two numbers?

A { x: Int, y: Int -> x + y }

B (x, y) => x + y

C fun(x, y) { return x + y }

D lambda x, y: x + y

Option A is the correct Kotlin lambda syntax. Options A and D are from other languages, and C is a function, not a lambda.

How do you call a lambda stored in a variable named multiply with arguments 3 and 4?

A multiply->(3,4)

B multiply.call(3, 4)

C multiply(3, 4)

D call multiply(3,4)

In Kotlin, you call a lambda like a normal function using parentheses and arguments.

What does the it keyword represent in a Kotlin lambda?

A The single implicit parameter of the lambda

B The return value of the lambda

C A keyword to exit the lambda

D A variable declared outside the lambda

it is used as the name of the single parameter when a lambda has exactly one parameter.

Which of these is NOT a valid way to declare a lambda in Kotlin?

A val f = { x: Int -> x * 2 }

B val f: (Int) -> Int = { x -> x * 2 }

C val f = fun(x: Int) = x * 2

D val f = lambda x: x * 2

Option D uses Python-like syntax which is invalid in Kotlin.

What is the return type of a Kotlin lambda that looks like { a: Int, b: Int -> a + b }?

A Nothing

B Int

C String

D Unit

The lambda returns the sum of two integers, so its return type is Int.

Explain how to declare and use a lambda in Kotlin that takes one parameter and returns its square.

Think about how to write the lambda and how to call it with a number.

Describe the difference between a lambda expression and a regular function in Kotlin.

Focus on how lambdas are unnamed and can be stored or passed around easily.