indexOf
Returns first index of element, or -1 if the array does not contain element.
fun <T> Array<out T>.indexOf(element: T): Int(source)
fun main() {
val fruits = arrayOf("apple", "banana", "cherry")
val index = fruits.indexOf("banana")
println(index) // prints 1
val missingIndex = fruits.indexOf("orange")
println(missingIndex) // prints -1
}