Queue using a fixed size array

gistfile1.rb

class Queue

  def initialize(size=10)
    raise 'InvalidInputType' unless size.is_a?(Fixnum)
    @store = Array.new(size)
    @size = size
    @tail = @head = 0 
  end

  def enqueue(ele)
    raise "Overflow" if full?
    @store[@tail] = ele
    if @tail == @size - 1
      @tail = 0
    else
      @tail += 1
    end 
  end

  def dequeue
    raise "Underflow" if empty?

    result = @store[@head]
    @store[@head] = nil 
    if @head == @size - 1
        @head = 0
    else
      @head += 1
    end

    result
  end

  def empty?
    @head == @tail
  end 

  def full?
    @head == @tail + 1
  end

end