PathWalkOption

val startDirectory = createTempDirectory()
run {
    (startDirectory / "1" / "2" / "3" / "4").createDirectories()
    (startDirectory / "1" / "2" / "3" / "a.txt").createFile()
    (startDirectory / "1" / "2" / "b.txt").createFile()
    (startDirectory / "c.txt").createFile()
}

// Default walk options. Prints:
//    1/2/b.txt
//    1/2/3/a.txt
//    c.txt
startDirectory.walk().forEach { path ->
    println(path.relativeTo(startDirectory))
}

// Custom walk options. Prints:
//    1
//    c.txt
//    1/2
//    1/2/b.txt
//    1/2/3
//    1/2/3/a.txt
//    1/2/3/4
startDirectory.walk(PathWalkOption.INCLUDE_DIRECTORIES, PathWalkOption.BREADTH_FIRST).forEach { path ->
    println(path.relativeTo(startDirectory))
}