Queue with an expanding buffer

queue.rb

class Queue
  attr_reader :elements

  def initialize
    @elements = Buffer.new
  end

  def push(element)
    @elements << element
  end

  def pop
    @elements.pop
  end

  def peek
    @elements.peek
  end

  def size
    @elements.size
  end

  def empty?
    @elements.empty?
  end
end

class Buffer < Array                                                                                                                                                                                [3/1847]
  def initialize
    @current = 0
    @insert = 0
    super
  end

  def <<(val)
    update_insert_index!
    self[@insert] = val
    @insert += 1
  end

  def pop
    update_current_index!
    item = self[@current]
    self[@current] = nil
    @current += 1
    item
  end

  def peek
    self[current_index]
  end

  def size
    self.compact.size
  end

  def empty?
    self.compact.empty?
  end

  private

  def update_current_index!
    @current = current_index
  end

  def current_index
    return 0 if @current == self.to_a.size
    @current
  end

  def update_insert_index!
    if @current > 0
      @insert = 0 if @insert == self.to_a.size
      while !self[@insert].nil?
        if @insert == @current
          new_array = Array.new(self.to_a.size)
          self.insert(@insert, *new_array)
          @current += new_array.size
        else
          @insert += 1
        end
      end
    end
  end
end

queue_spec.rb

require File.join(File.dirname(__FILE__), 'queue')

describe Queue do
  before(:each) do
    @queue = Queue.new
  end

  it "should be able to push things on the queue" do
    @queue.push(1)

    @queue.size.should == 1
  end

  it "should pop of the first item on the queue" do
    @queue.push(1)
    @queue.push(2)

    @queue.pop.should == 1
    @queue.size.should == 1
  end

  it "should be able to get the next element without removing it" do
    @queue.push(1)

    @queue.peek.should == 1
    @queue.size.should == 1
  end

  it "should know if it's empty" do
    @queue.should be_empty

    @queue.push(1)
    @queue.pop

    @queue.should be_empty

    @queue.push(1)

    @queue.should_not be_empty
  end

  it "should not adjust the length of the internal array if not needed" do
    @queue.push(1)
    @queue.push(2)
    @queue.push(3)
    @queue.push(4)
    @queue.push(5)

    @queue.elements.size.should == 5

    @queue.pop.should == 1
    @queue.pop.should == 2

    @queue.elements.size.should == 3

    @queue.push(6)
    @queue.push(7)
    @queue.push(8)

    @queue.elements.size.should == 6

    @queue.pop.should == 3
    @queue.pop.should == 4
    @queue.pop.should == 5
    @queue.pop.should == 6
    @queue.pop.should == 7
    @queue.pop.should == 8

    @queue.push(9)
    @queue.pop.should == 9

    @queue.elements.size.should == 0
  end
end