How to insert an element after another using a LinkedHashSet in Kotlin - kotlin

Question

I am trying to search for a collection type that have the following properties:
Maintain insertion order
Don't allow duplicates
Add one or more elements after another
I could create my own data collection but I wish not to.
After taking a look at all collections available in kotlin I think LinkedHashSet have almost all of my requirements, however it can't add elements after another or at nth position.
Is there any way to accomplish this with an extension method or any another trick?

Answer 1

You can just use List<> or any of its implementations. Its maintain insertion order, you can add one or more elements after another, and you can accomplish the "avoid duplicates" requirement by calling .distinct() when returning your list. i.e:
private fun fillData(): MutableList<String> {
var dataSet: MutableList<String> = ArrayList()
for (i in 0..10) dataSet.add("Product $i")
dataSet.add("aaa")
dataSet.add("aaa")
dataSet.add("aaa")
dataSet.add("aaa")
dataSet.add("aaa")
return dataSet.distinct().toMutableList()
}
The result of this function returns an array with 11 elements, "Product 1".. "Product 10" and just 1 "aaa" element at the end.
you can see the doc of List.distinct() here

Answer 2

In the standard library (& Java collection API) there isn't such a collection type as far as I know.
Apache commons collections however contains what you are looking for: ListOrderedSet

Answer 3

Why not implement a custom data structure that exactly serve your requirements?
class OrderedHashSet<E> : MutableSet<E>{
private val set = HashSet<E>()
private val list = LinkedList<E>()
override val size: Int
get() = list.size
override fun contains(element: E) = set.contains(element)
override fun containsAll(elements: Collection<E>) = set.containsAll(elements)
override fun isEmpty() = list.isEmpty()
override fun iterator() = list.iterator()
override fun add(element: E): Boolean {
if(set.add(element)){
list.add(element)
return true
}
return false
}
fun add(index: Int, element: E) : Boolean {
if(set.add(element)){
list.add(index, element)
return true
}
return false
}
override fun addAll(elements: Collection<E>): Boolean {
var modified = false
for(element in elements){
if(add(element)){
modified = true
}
}
return modified
}
override fun clear() {
set.clear()
list.clear()
}
override fun remove(element: E): Boolean {
set.remove(element)
return list.remove(element)
}
override fun removeAll(elements: Collection<E>): Boolean {
var modified = false
for(element in elements){
if(remove(element)){
modified = true
}
}
return modified
}
override fun retainAll(elements: Collection<E>): Boolean {
set.retainAll(elements)
return list.retainAll(elements)
}
}