Insertion-ordered ListSet

collection.mutable.LinkedHashSet is a set that iterates its members in the same sequence they were inserted. (I avoid the term "ordered" here, since I prefer to reserve that to cases of an ordering relation on the values, not the particular sequence in which some actions were carried out.)

var eti = a.toList.reverse.iterator

It is not ordered:

val a = ListSet(3,1,2)
val ite = a.iterator
ite.next // returns 2
ite.next // returns 1
ite.next // returns 3