code: func newKeyedDeque() *keyedDeque {
  	return &keyedDeque{
  		RWMutex:       &sync.RWMutex{},
  		syncedList:    newSyncedList(),
  		index:         make(map[interface{}]*list.Element),
  		invertedIndex: make(map[*list.Element]interface{}),
  	}
  }
docs: // newKeyedDeque returns a newKeyedDeque pointer.