retainAll
Retains only the elements in this collection that are contained in the specified collection.
@IgnorableReturnValueinline fun <T> MutableCollection<out T>.retainAll(elements: Collection<T>): Boolean(source)
fun main() {
val numbers = mutableListOf(1, 2, 3, 4, 5)
val toKeep = listOf(2, 4, 6)
val wasModified = numbers.retainAll(toKeep)
println("Modified: $wasModified")
println("Resulting list: $numbers")
}