buildSet

Builds a new read-only Set by populating a MutableSet using the given builderAction and returning a read-only set with the same elements.

inline fun <E> buildSet(builderAction: MutableSet<E>.() -> Unit): Set<E>(source)

fun main() {
    val fruits: Set<String> = buildSet {
        add("apple")
        add("banana")
        add("orange")
    }
    println(fruits) // [apple, banana, orange]
}

Source