[Kotlin] Generic Functions

//vararg: just like ...args in js
class Stack<T>(vararg val items: T) {
    
    val elements = items.toMutableList()
    
    fun push(element: T) {
        elements.add(element)
    }
    
    fun pop(): T? {
        if (!isEmpty()) {
            return elements.removeAt(elements.size - 1)
        }
        return null
    }
    
    fun isEmpty(): Boolean {
        return elements.isEmpty()
    }
}

fun <T> stackOf(vararg elements: T): Stack<T> {
    return Stack(*elements) // spread opeator *
}


fun main() {
    val stack = Stack(3,4,2,6)
    println(stack.pop())
    println(stack.pop())
    println(stack.pop())
    println(stack.pop())
    println(stack.pop()) // null
    
    val stack2 = stackOf("HI", "Hello", "Bye")
    
    for(i in 1..3) {
        println(stack2.pop())
    }
}