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A List is a sequence of elements of the same data type, which may contain duplicate values. Elements can be inserted, fetched and removed from a list.

By default a list is empty, meaning that it has no elements. However, you can use the system actions to manipulate an empty list.

On the server side, variables of List data type have a reference to the values and don't contain a copy of the elements. For example, if you have two lists List A and List B and you assign List A to the List B, you will have two variables pointing to the same list instead of two independent copies. When changing values in one variable, the other is also changed.

Runtime Properties

OutSystems provides the following runtime properties for lists:

Property Type Access type Comment
Current List element type Read/write Allows direct access to the current element.
EOF Boolean Read only Indicates whether the end of the list was exceeded. When you are iterating the last element, this property is still FALSE.
BOF Boolean Read only Indicates whether you are at the beginning of the list. When you are iterating the first element, this property is True.
CurrentRowNumber Integer Read only The index of the current element in the list, starting with 0.
If the list is empty, this property is 0.
Length Integer Read only The number of elements currently in the list.
Empty Boolean Read only Indicates whether the list is empty.

List System Actions

The following System Actions are available to manipulate a List:

System Action Description
ListAll Determines if all the elements in the list satisfy the given condition.
ListAny Determines if any of the elements in the list satisfies the given condition.
ListAppend Adds an element to the end of a list.
ListAppendAll Adds the elements of the source list to the end of the destination list.
ListClear Removes all elements from a list.
ListDuplicate Duplicates the elements of a list into another list.
ListFilter Produces a new list with the elements of the source list that satisfy the given condition.
ListIndexOf Returns the position of the first element that satisfies the given condition, or -1 if no element was found.
ListInsert Inserts an element in a specific position of a list.
ListRemove Removes an element from a specific position of a list.
ListSort Sorts the elements in the list by the given criteria.
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