require File.expand_path('../websocket', __FILE__) unless defined?(Faye::WebSocket) #可以把路径转换成绝对路径

module Faye
  class EventSource

    include WebSocket::API::EventTarget
    attr_reader :env, :url, :ready_state

    DEFAULT_RETRY = 5

    def initialize(env, options = {})
      WebSocket.ensure_reactor_running
      super()

      @env    = env
      @ping   = options[:ping]
      @retry  = (options[:retry] || DEFAULT_RETRY).to_f
      @url    = EventSource.determine_url(env)
      @stream = Stream.new(self)

      @ready_state = WebSocket::API::CONNECTING

      headers = ::WebSocket::Driver::Headers.new
      if options[:headers]
        options[:headers].each { |k,v| headers[k] = v }
      end

      if callback = @env['async.callback']
        callback.call([101, {}, @stream])
      end

      @stream.write("HTTP/1.1 200 OK\r\n" +
                    "Content-Type: text/event-stream\r\n" +
                    "Cache-Control: no-cache, no-store\r\n" +
                    "Connection: close\r\n" +
                    headers.to_s +
                    "\r\n" +
                    "retry: #{ (@retry * 1000).floor }\r\n\r\n")

      EventMachine.next_tick { open }

      if @ping
        @ping_timer = EventMachine.add_periodic_timer(@ping) { ping }
      end
    end
  end
end

这里的headers = ::WebSocket::Driver::Headers.new中的::表示什么？ 他和headers = WebSocket::Driver::Headers.new这样写有什么区别？ 谢谢