Lambda with receiver concept in Kotlin - Mini Project: Build & Apply

Lambda with receiver concept

📖 Scenario: Imagine you want to build a simple text formatter that can change the case of a string and add punctuation. Using Kotlin's lambda with receiver, you can create a neat way to apply these changes inside a block that feels like working directly on the string.

🎯 Goal: You will create a lambda with receiver that modifies a string by changing its case and adding punctuation, then apply it to a sample string and print the result.

📋 What You'll Learn

Create a variable called text with the value "hello kotlin"

Create a lambda with receiver called formatter of type String.() -> String

Inside formatter, convert the string to uppercase and add an exclamation mark at the end

Call formatter on text and store the result in formattedText

Print the value of formattedText

💡 Why This Matters

🌍 Real World

Lambda with receiver is useful in Kotlin DSLs (domain-specific languages) and builder patterns where you want to write clean and readable code that looks like it is working inside an object.

💼 Career

Understanding lambda with receiver helps you work with Kotlin libraries and frameworks that use this feature, such as Android development with Kotlin, making your code more concise and expressive.

1

Create the initial string

Create a variable called text and set it to the string "hello kotlin".

Kotlin

# Create a variable called text with value "hello kotlin"
# Your code here

Need a hint?

Use val text = "hello kotlin" to create the string variable.

2

Create the lambda with receiver

Create a lambda with receiver called formatter of type String.() -> String. Inside it, convert the string to uppercase and add an exclamation mark at the end.

Kotlin

val text = "hello kotlin"
# Create a lambda with receiver called formatter of type String.() -> String
# Inside it, convert the string to uppercase and add an exclamation mark
# Your code here

Need a hint?

Define formatter as val formatter: String.() -> String = { this.uppercase() + "!" }.

3

Apply the lambda with receiver

Call the lambda formatter on the variable text and store the result in a variable called formattedText.

Kotlin

val text = "hello kotlin"
val formatter: String.() -> String = { this.uppercase() + "!" }
# Call formatter on text and store the result in formattedText
# Your code here

Need a hint?

Use val formattedText = text.formatter() to apply the lambda.

4

Print the formatted text

Print the value of the variable formattedText.

Kotlin

val text = "hello kotlin"
val formatter: String.() -> String = { this.uppercase() + "!" }
val formattedText = text.formatter()
# Print formattedText
# Your code here

Need a hint?

Use println(formattedText) to display the result.