Insert node at beginning of linked list in ruby

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

Here given of code implementation process.

#  Ruby program for
#  Insert node at beginning of linked list

#  Linked list node
class LinkNode 
    # Define the accessor and reader of class LinkNode
    attr_reader :data, :next
    attr_accessor :data, :next
    def initialize(data) 
        self.data = data
        self.next = nil
    end

end

class SingleLL 
    # Define the accessor and reader of class SingleLL
    attr_reader :head
    attr_accessor :head
    def initialize() 
        self.head = nil
    end

    #  Adding new node at beginning of linked list
    def addNode(data) 
        #  Create new node
        node = LinkNode.new(data)
        #  Connect current node to previous head
        node.next = self.head
        self.head = node
    end

    #  Display linked list element
    def display() 
        if (self.head == nil) 
            return
        end

        temp = self.head
        #  iterating linked list elements
        while (temp != nil) 
            print(temp.data ," → ")
            #  Visit to next node
            temp = temp.next
        end

        print(" NULL\n")
    end

end

def main() 
    sll = SingleLL.new()
    #  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()
end

main()

 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → NULL

Time complexity of above program is O(1).