Other nice thing I would suggest: Allow to actual implement a header with a default implementation. A possible use case is this one:

header fun ByteArray.copyRangeTo(srcPos: Int, dst: ByteArray, dstPos: Int, count: Int) {
	for (n in 0 until count) dst[dstPos + n] = this[srcPos + n]
}

Here I provide a generic implementation, that can be improved using System.arraycopy in JVM or the former for JS typed arrays, but as an optimization, not mandatory. So for example I wouldn’t have to implement for Konan at the very beginning and implement it later when optimizing things

Interesting idea! Please report it as a feature request at kotl.in/issue

Sorry. Didn’t notice this (I still have issues with slack notifications) I have created the issue already! https://youtrack.jetbrains.com/issue/KT-20427