Android Development with Kotlin

Extension functions under the hood

While Kotlin extension functions might look magical, they are really simple under the hood. A top-level extension function is compiled to a static function with a receiver object on the first argument. Let's look at the already presented toast function:

    // ContextExt.kt     fun Context.toast(text: String) { 
        Toast.makeText(this, text, LENGTH_LONG).show() 
    } 

This function, after compilation and decompilation to Java, will look similar to the following function:

//Java 
public class ContextExtKt { 
    public static void toast(Context receiver, String text) { 
        Toast.makeText(receiver, text, Toast.LENGTH_SHORT).show(); 
    } 
}

Kotlin top-level extension functions are compiled to static functions with a receiver object on ...