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kotlinlang

convinced everyone to use the 4...weird that Android Studio's default isn't 4.  The examples in the guides seem to prefer 4:

fun &lt;T&gt; Iterable&lt;T&gt;.joinToString(
    separator: CharSequence = ", ",
    prefix: CharSequence = "",
    postfix: CharSequence = ""
): String {

(though that's method call parameters vs. constructor params which the Android style guide doesn't cover)
and from the Kotlin style guide

class Person(
    id: Int,
    name: String,
    surname: String
) : Human(id, name) { ... }