class Sass::OrderedHash

def []=(key, value)
  node = Node.new(key, value)
  if old = @hash[key]
    if old.prev
      old.prev.next = old.next
    else # old is @first and @last
      @first = @last = nil
    end
  end
  if @first.nil?
    @first = @last = node
  else
    node.prev = @last
    @last.next = node
    @last = node
  end
  @hash[key] = node
  value
end