is there a list structure in Kotlin which keeps distinct values only?

e.g.  val list = listOf(3,9,1,6,7)

if I add a new 9, it would removes the old one:

list.add(9)
println(list) // listOf(3,1,6,7,9)

a set?

val set = setOf(3, 9, 1, 6, 7)

val set = mutableSetOf(3, 9, 1, 6, 7)
set.add(9)
println(set)

it still prints [3, 9, 1, 6, 7]

mutableSetOf() preserves insertion order. remove and re-add

I was hoping Kotlin already had a structure like that

it's not in any language's stdlib that I know of, partly because it's not that universal: all users wants slightly different things out of it

yep ^^