Challenge: toDragonSpeak Extension

Kotlin Programming: The Big Nerd Ranch Guide 18. Extensions
1

Here’s my solution. Any feedback would be welcomed!

fun main() {
    println("Kotlin Programming".toDragonSpeakExt())
}

private fun String.toDragonSpeakExt() =
    this.replace(Regex("[aeiouAEIOU]")) {
        when (it.value.toLowerCase()) {
            "a" -> "4"
            "e" -> "3"
            "i" -> "1"
            "o" -> "0"
            "u" -> "|_|"
            else -> it.value
        }
    }