Insert node at beginning of linked list in swift

Write a program which is create and add new node at the beginning of linked list in swift.

Here given of code implementation process.

/*
    Swift 4 program for
    Insert node at beginning of linked list
*/
// Linked list node
class LinkNode
{
    var data: Int;
    var next: LinkNode? ;
    init(_ data: Int, _ next: LinkNode? )
    {
        self.data = data;
        self.next = next;
    }
}
class SingleLL
{
    var head: LinkNode? ;
    init()
    {
        // Set inital value
        self.head = nil;
    }
    // Adding new node at beginning of linked list
    func addNode(_ data: Int)
    {
        // Create new node and set new head
        self.head = LinkNode(data, self.head);
    }
    // Display linked list element
    func display()
    {
        if (self.head == nil)
        {
            return;
        }
        var temp: LinkNode? = self.head;
        // iterating linked list elements
        while (temp  != nil)
        {
            print(temp!.data, terminator: " → ");
            // Visit to next node
            temp = temp!.next;
        }
        print(" NULL");
    }
}
func main()
{
    let sll: SingleLL = SingleLL();
    // Linked list
    // 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL
    sll.addNode(8);
    sll.addNode(7);
    sll.addNode(6);
    sll.addNode(5);
    sll.addNode(4);
    sll.addNode(3);
    sll.addNode(2);
    sll.addNode(1);
    sll.display();
}
main();

 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL

Time complexity of above program is O(1).