Lambda with receiver concept in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a lambda with receiver in Kotlin?

A lambda with receiver is a special kind of lambda where you can call methods and access properties of a receiver object directly inside the lambda, without using its name.

intermediate

How do you define a lambda with receiver type in Kotlin?

You define it by specifying the receiver type before the lambda parameters, like ReceiverType.() -> ReturnType. For example, String.() -> Int means a lambda that acts on a String receiver and returns an Int.

beginner

What is the benefit of using a lambda with receiver?

It lets you write cleaner and more readable code by calling receiver's methods directly inside the lambda, similar to how you use this in a class, reducing repetition.

intermediate

How do you call a lambda with receiver?

You call it by providing the receiver object and then invoking the lambda on it. For example, val result = receiver.lambda() where lambda is a lambda with receiver.

beginner

Example: What does this Kotlin code print?<br>

val greet: String.() -> String = { "Hello, $this!" }
println("World".greet())

It prints Hello, World! because the lambda uses the receiver String ("World") as this and returns the greeting.

What keyword represents the receiver object inside a lambda with receiver?

A this

B it

C self

D receiver

Inside a lambda with receiver, the receiver object is accessed using the keyword this.

Which of the following is a correct type for a lambda with receiver that acts on Int and returns String?

A () -> String

B (Int) -> String

C Int.() -> String

D String.() -> Int

The correct syntax for a lambda with receiver is ReceiverType.() -> ReturnType, so Int.() -> String is correct.

What is the main advantage of using lambda with receiver?

A Improves performance by compiling to native code

B Allows calling receiver's methods without naming the receiver

C Enables multi-threading automatically

D Prevents null pointer exceptions

Lambda with receiver lets you call methods and properties of the receiver directly, making code cleaner.

Given val action: String.() -> Unit = { println(this) }, how do you invoke it on "Hello"?

A "Hello".action()

B action.invoke("Hello")

C action("Hello")

D action.call("Hello")

You invoke a lambda with receiver by calling it on the receiver object, like "Hello".action().

In a lambda with receiver, what does this refer to?

A The first parameter

B The lambda itself

C The outer class instance

D The receiver object

this inside a lambda with receiver refers to the receiver object on which the lambda is called.

Explain what a lambda with receiver is and how it differs from a regular lambda.

Think about how you can call methods inside the lambda without naming the object.

Describe how to define and invoke a lambda with receiver in Kotlin with a simple example.

Use a String receiver and a lambda that returns a greeting.