code: func (list *LinkedList) String() string {
  	list.key.RLock()
  	defer list.key.RUnlock()
  
  	builder := bytes.NewBufferString("[")
  	current := list.first
  	for i := 0; i < 15 && current != nil; i++ {
  		builder.WriteString(fmt.Sprintf("%v ", current.payload))
  		current = current.next
  	}
  	if current == nil || current.next == nil {
  		builder.Truncate(builder.Len() - 1)
  	} else {
  		builder.WriteString("...")
  	}
  	builder.WriteRune(']')
  	return builder.String()
  }
docs: // String prints upto the first fifteen elements of the list in string format.