Change main to accept Array<out String>

[JakeWharton]

Since it never mutates the array and simply creates a list, main(args: Array<String>) should ideally be main(args: Array<out String>). This will improve the compatibility with the three ways you can define the parameter for a normal main method.

Here's an illustrative example:

fun testMain(vararg varargString: String) {
  val arrayString: Array<String> = emptyArray()
  val arrayOutString: Array<out String> = emptyArray()
  
  exampleNoOut(varargString)
  exampleNoOut(arrayString)
  exampleNoOut(arrayOutString)
  
  exampleOut(varargString)
  exampleOut(arrayString)
  exampleOut(arrayOutString)
}

fun exampleNoOut(args: Array<String>) = Unit
fun exampleOut(args: Array<out String>) = Unit

And what it looks like in the IDE:

This is a binary-compatible change since variance is a concept solely implemented in the compiler (like generics in general). It also should be a source-compatible change as you can see above, but also because Array<out String> is more permissive than Array<String> in what it accepts.

[ajalt]

TIL that you can declare main as vararg. The bytecode's the same, so it makes sense, but I've never seen it mentioned in any docs.

[JakeWharton]

Same is true of Java!

public static void main(String... args) {
}