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Mastering Kotlin Essentials

Extension Functions and Properties

Explore Kotlin’s extension functions and properties, gaining insights into their working.

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Extension functions

Let’s examine the Java bytecode generated from a Kotlin extension function:

Kotlin 1.5
fun String.remove(value: String) = this.replace(value, "")
fun main() {
    println("A B C".remove(" ")) // ABC
}

As a result, we should see the following code:

Java
final class PlaygroundKt {
    public static final String remove(
            String $this$remove,
            String value
    ) {
        // Null-check using a conditional operator
        $this$remove = ($this$remove != null) ? $this$remove : "";
        value = (value != null) ? value : "";
        // Use standard Java replace method
        return $this$remove.replace(value, "");
    }
    public static void main(String[] args) {
        // parameter not-null check
        String var1 = remove("A B C", " ");
        System.out.println(var1);
    }
}
...