listappendlist

Listappendlist is a term used in discussions of list processing to denote the operation of appending one list to another. The operation combines two lists into a single list by placing the elements of the second list after the elements of the first. It can be performed in-place, mutating the first list, or it can produce a new list without altering the inputs.

In the in-place variant, the first list is extended by adding each element of the second list to its end. In the non-mutating variant, a new list is created that contains all elements from both lists in order, leaving the original lists unchanged.

Complexity considerations are similar to other list operations. The time cost is proportional to the total number of elements, typically O(n + m) for lists of lengths n and m. Space usage depends on the variant: in-place listappendlist requires O(1) additional space beyond the input lists, while the non-mutating variant requires O(n + m) extra space for the new list.

Relation to existing terminology varies by language. In many languages, the in-place version corresponds to an extend or append operation on the first list, while the non-mutating version resembles a concatenation operation that yields a new list. Some languages treat appending a list as a single element when using a plain append, so careful distinction between extending a list and appending a list as a single element is important.

Examples: given A = [1, 2] and B = [3, 4], in-place listappendlist(A, B) yields A = [1, 2, 3, 4], with B unchanged; a non-mutating form returns [1, 2, 3, 4] while leaving A and B intact.

Notes: the term is informal and not standardized across programming languages. See also: extend, concatenate, append, merge.