code: func Pop(queue Queue) interface{} {
  	var result interface{}
  	queue.Pop(func(obj interface{}) error {
  		result = obj
  		return nil
  	})
  	return result
  }
docs: // Helper function for popping from Queue.
  // WARNING: Do NOT use this function in non-test code to avoid races
  // unless you really really really really know what you are doing.