Linked List in Ruby

linked_list.rb

class LinkedList

  include Enumerable

  def initialize
    @first = Node.new nil
    @last = Node.new nil

    @first.next = @last
    @last.prev = @first
    @size = 0
  end

  def addLast(object)
    node = Node.new(object)
    node.next = @last
    node.prev = @last.prev
    
    @last.prev.next = node
    @last.prev = node
    @size += 1
  end

  def addFirst(object)
    node = Node.new(object)
    node.prev = @first
    node.next = @first.next
    
    @first.next.prev = node
    @first.next = node
    @size += 1
  end

  def last
    if @size <= 0
      raise "No objects in list"
    end

    return @last.prev.object
  end

  def first
    if @size <= 0
      raise "No objects in list"
    end

    return @first.next.object
  end

  def removeLast
    if @size <= 0
      raise "No objects in list"
    end

    node = @last.prev
    node.prev.next = @last
    @last.prev = node.prev
    @size -= 1

    return node.object
  end

  def removeFirst
    if @size <= 0
      raise "No objects in list"
    end

    node = @first.next
    node.next.prev = @first
    @first.next = node.next
    @size -= 1

    return node.object
  end

  def size
    return @size
  end

  def each
    node = @first.next
    while node != @last
      yield node.object
      node = node.next
    end
  end

  def reverse_each
    node = @last
    loop do
      yield node.object
      node = node.prev
      if ! node
        break
      end
    end
  end

  class Node
    
    attr_reader :object
    attr_reader :prev
    attr_reader :next
    
    attr_writer :next
    attr_writer :prev

    def initialize(object)
      @object = object
    end

    def dump(io)
      io.puts "===== #{self} ====="
      io.puts "Object: #{@object}"
      io.puts "Prev: #{@prev}"
      io.puts "Next: #{@next}"
    end
  end

end