Nullable receiver extensions in Kotlin - Mini Project: Build & Apply

Nullable Receiver Extensions

📖 Scenario: Imagine you are building a simple app that processes user comments. Sometimes, the comment text might be missing (null). You want to safely check if a comment is empty or not, even if the comment itself is null.

🎯 Goal: Create a Kotlin extension function with a nullable receiver that checks if a string is null or empty. Then use it to safely check comments.

📋 What You'll Learn

Create a nullable receiver extension function called isNullOrEmptyCustom for String?

The function should return true if the string is null or empty, otherwise false

Create a list of nullable strings called comments with exact values: "Hello", "", null, "Kotlin"

Use a for loop with variables comment to iterate over comments

Inside the loop, print "Empty or null" if comment.isNullOrEmptyCustom() is true, else print the comment text

💡 Why This Matters

🌍 Real World

Nullable receiver extensions help safely add functions to types that can be null, avoiding crashes and making code cleaner.

💼 Career

Understanding nullable receiver extensions is important for Kotlin developers to write safe and readable code, especially when dealing with optional data.

1

Create the list of nullable comments

Create a list called comments with these exact nullable string values: "Hello", "", null, "Kotlin"

Kotlin

# Create the list called comments with the exact values
# Your code here

Need a hint?

Use listOf to create a list with nullable strings.

2

Create the nullable receiver extension function

Create an extension function called isNullOrEmptyCustom with a nullable String? receiver that returns true if the string is null or empty, otherwise false

Kotlin

val comments: List = listOf("Hello", "", null, "Kotlin")

// Create the extension function isNullOrEmptyCustom for String? below
# Your code here

Need a hint?

Use fun String?.isNullOrEmptyCustom() to define the extension function with nullable receiver.

3

Use a for loop to check each comment

Use a for loop with variable comment to iterate over comments. Inside the loop, use comment.isNullOrEmptyCustom() to check if the comment is empty or null.

Kotlin

val comments: List = listOf("Hello", "", null, "Kotlin")

fun String?.isNullOrEmptyCustom(): Boolean {
    return this == null || this.isEmpty()
}

// Add a for loop to iterate over comments and check each comment
# Your code here

Need a hint?

Use for (comment in comments) to loop, then if (comment.isNullOrEmptyCustom()) to check.

4

Print the results

Print the output inside the loop as specified: print "Empty or null" if comment.isNullOrEmptyCustom() is true, otherwise print the comment text.

Kotlin

val comments: List = listOf("Hello", "", null, "Kotlin")

fun String?.isNullOrEmptyCustom(): Boolean {
    return this == null || this.isEmpty()
}

for (comment in comments) {
    if (comment.isNullOrEmptyCustom()) {
        // Print "Empty or null" here
    } else {
        // Print the comment here
    }
}

Need a hint?

Use println to print the correct output inside the loop.