Set

A set is an unordered collection that does not support duplicates. For creating sets, there are functions setOf() and mutableSetOf(). A read-only view of a mutable set can be obtained by casting it to Set.

val openIssues: MutableSet<String> = mutableSetOf("uniqueDescr1", "uniqueDescr2", "uniqueDescr3") // 1

fun addIssue(uniqueDesc: String): Boolean {                                                       
    return openIssues.add(uniqueDesc)                                                             // 2
}

fun getStatusLog(isAdded: Boolean): String {                                                       
    return if (isAdded) "registered correctly." else "marked as duplicate and rejected."          // 3
}

fun main() {
    val aNewIssue: String = "uniqueDescr4"
    val anIssueAlreadyIn: String = "uniqueDescr2" 

    println("Issue $aNewIssue ${getStatusLog(addIssue(aNewIssue))}")                              // 4
    println("Issue $anIssueAlreadyIn ${getStatusLog(addIssue(anIssueAlreadyIn))}")                // 5 
}

1. Creates a Set with given elements.
2. Returns a boolean value showing if the element was actually added.
3. Returns a string, based on function input parameter.
4. Prints a success message: the new element is added to the Set.
5. Prints a failure message: the element can't be added because it duplicates an existing element.