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[] args) {
   Intrinsics.checkParameterIsNotNull(args, "args");
   Integer value = StringsKt.toIntOrNull(args[0]);
byte var2 = 0;
if (CollectionsKt.contains((Iterable)(new IntRange(var2, 10)), value)) {
  ...