code: func (q *UniqueQueue) Head() (TimedValue, bool) {
  	q.lock.Lock()
  	defer q.lock.Unlock()
  	if len(q.queue) == 0 {
  		return TimedValue{}, false
  	}
  	result := q.queue[0]
  	return *result, true
  }
docs: // Head returns the oldest added value that wasn't returned yet
  // without removing it.