Method LTrim

structure/list.go:363–405

LTrim retains a range of elements in a list associated with a key. The range is inclusive, including both the start and stop indices. If the key does not exist, an error is returned. If the list is empty, an error is returned. Negative indices can be used, where -1 represents the last element of the

(key string, start int, stop int)

// Negative indices can be used, where -1 represents the last element of the list,
// -2 represents the second last element, and so on.
func (l *ListStructure) LTrim(key string, start int, stop int) error {
	// Get the list
	lst, _, err := l.getListFromDB(key, false)
	if err != nil {
		return err
	}
	if lst.Length == 0 {
		return ErrListEmpty
	}

	// Calculate the correct indices
	start = (start%lst.Length + lst.Length) % lst.Length
	stop = (stop%lst.Length + lst.Length) % lst.Length

	if start > stop {
		lst = &list{
			Head:   nil,
			Length: 0,
		}
	} else {
		// Find the new head
		newHead := lst.Head
		for i := 0; i < start; i++ {
			newHead = newHead.Next
		}

		// Find the new tail
		newTail := newHead
		for i := start; i < stop; i++ {
			newTail = newTail.Next
		}

		// Disconnect the new tail from the rest of the list
		newTail.Next = nil

		// Update the list
		lst.Head = newHead
		lst.Length = stop - start + 1
	}

	// Store in the database
	return l.setListToDB(key, lst, 0)
}

// LIndex returns the value of an element in a list associated with a key based on the index.
// If the key does not exist, an error is returned.