Higher-order function declaration in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a higher-order function in Kotlin?

A higher-order function is a function that takes another function as a parameter or returns a function as a result.

beginner

How do you declare a higher-order function that takes a function as a parameter in Kotlin?

You specify the parameter type as a function type, for example: <br>fun operate(x: Int, y: Int, op: (Int, Int) -> Int): Int

intermediate

What does this Kotlin function declaration mean?<br>fun applyTwice(x: Int, f: (Int) -> Int): Int

It means the function applyTwice takes an integer x and a function f that takes an integer and returns an integer, then returns an integer.

intermediate

Can a higher-order function return another function in Kotlin? Give an example.

Yes. Example:<br>fun makeAdder(x: Int): (Int) -> Int { return { y -> x + y } }<br>This returns a function that adds x to its input.

beginner

Why are higher-order functions useful in Kotlin?

They allow you to write flexible and reusable code by passing behavior as parameters or returning behavior, enabling functional programming styles.

Which of the following is a correct Kotlin higher-order function declaration?

A fun compute(x: Int, f: Int): Int

B fun compute(x: Int, f: function): Int

C fun compute(x: Int, f: Int -> Int): Int

D fun compute(x: Int, f: (Int) -> Int): Int

Option D correctly declares a function that takes an Int and a function from Int to Int as parameters.

What does the function type (Int, Int) -> Int represent?

A A function taking two Ints and returning an Int

B A function taking one Int and returning two Ints

C A function returning a pair of Ints

D A function taking no parameters and returning Int

It represents a function that takes two Int parameters and returns an Int.

Can a Kotlin higher-order function return a function?

A Only if the function is anonymous

B No, Kotlin functions cannot return functions

C Yes, Kotlin supports returning functions

D Only if the function is inline

Kotlin supports functions returning other functions as part of its functional programming features.

What keyword is used to declare a function in Kotlin?

A def

B fun

C function

D func

The keyword fun is used to declare functions in Kotlin.

In Kotlin, how do you call a higher-order function that takes a lambda as a parameter?

A Pass the lambda expression inside curly braces after the function call

B Pass the lambda as a string

C You cannot pass lambdas to functions

D Use the keyword 'lambda' before the function name

You pass the lambda expression inside curly braces after the function call or as a parameter.

Explain how to declare a higher-order function in Kotlin that takes a function as a parameter.

Think about how you specify a parameter that itself is a function.

Describe a real-life example where a higher-order function might be useful in Kotlin programming.

Consider situations like sorting or filtering where you want to customize behavior.