Mastering High Performance with Kotlin

Ranges

Don't use nullable types with ranges. Let's look at the following example:

fun main(args: Array<String>) {    val int = args[0].toInt()    if (int in 0..10) {        println(int)    }}

This code, when decompiled to Java, looks as follows:

public static final void main(@NotNull String[] args) {   Intrinsics.checkParameterIsNotNull(args, "args");   String var2 = args[0];   int value = Integer.parseInt(var2);   if (0 <= value) {      if (10 >= value) {         System.out.println(value);      }   }}

As you can see, there's no overhead here. But if we use a nullable integer:

fun main(args: Array<String>) {    val value = args[0].toIntOrNull()    if (value in 0..10) {        println(value)    }}

Then this code, when decompiled to Java, looks as follows:

public static final void main(@NotNull String[] ...