kotlin - shuffle() vs shuffled()

shuffled()는 list를 shuffle한 결과를 새로운 list로 반환한다.
shuffle()은 list를 shuffle한 결과를 object에 저장한다.

list값이 변경되기에 mutableList에서만 사용가능 하다.

>>> listOf('1','2','3').shuffle()
error: unresolved reference. None of the following candidates is applicable because of receiver type mismatch: 
public inline fun <T> MutableList<???>.shuffle(): Unit defined in kotlin.collections
public inline fun <T> MutableList<???>.shuffle(random: java.util.Random): Unit defined in kotlin.collections
public fun <T> MutableList<???>.shuffle(random: kotlin.random.Random): Unit defined in kotlin.collections
listOf('1','2','3').shuffle()
                    ^
>>>  mutableListOf('1','2','3').shuffle()