{expr1} and {expr2} must be both Lists or both Dictionaries.

If they are Lists: Append {expr2} to {expr1}. If {expr3} is given insert the items of {expr2} before the item with index {expr3} in {expr1}. When {expr3} is zero insert before the first item. When {expr3} is equal to len({expr1}) then {expr2} is appended. Examples:

:echo sort(extend(mylist, [7, 5]))
:call extend(mylist, [2, 3], 1)

When {expr1} is the same List as {expr2} then the number of items copied is equal to the original length of the List. E.g., when {expr3} is 1 you get N new copies of the first item (where N is the original length of the List). Use add() to concatenate one item to a list. To concatenate two lists into a new list use the + operator:

:let newlist = [1, 2, 3] + [4, 5]

If they are Dictionaries: Add all entries from {expr2} to {expr1}. If a key exists in both {expr1} and {expr2} then {expr3} is used to decide what to do: {expr3} = "keep": keep the value of {expr1} {expr3} = "force": use the value of {expr2} {expr3} = "error": give an error message When {expr3} is omitted then "force" is assumed.

{expr1} is changed when {expr2} is not empty. If necessary make a copy of {expr1} first. {expr2} remains unchanged. When {expr1} is locked and {expr2} is not empty the operation fails. Returns {expr1}. Returns 0 on error.

Can also be used as a method:

mylist->extend(otherlist)