Definition of List, Set, Container, and Map

 

Difference between List, Set, Container, and Map

Containers:

Containers are dynamic and have no limits. They can contain elements of
almost all data types: boolean, integer, real, date, string, container,
arrays, tables, and extended data types. However, objects may not be stored
in containers.

Containers in AX are used very often. It’s easy to work with them. But…
data in containers are stored sequentially and thus retrieved sequentially.
This means that containers provide slower data access if you are working with
_large numbers_ of records. In case of large numbers of records use temporary
tables.

List:

Lists are structures that may contain any number of elements that are
accessed sequentially. Lists may contain values of any X++ type. All the
values in the list must be of __the same__(this is the main difference
between lists and containers) type, given in the creation of the list. The
implementation of lists is such that the traversal of the list elements is __very
fast.

Take a look for example at the class Dialog addControl() method.
Their controls are stored in ctrls List.

Map:

A map is a data type that associates one (key) value with another value [An
analog – a small table in memory with two fields: Keys, Values]. Both the key
and value values may be of any valid X++ type, including objects. The types
of the key and the value are given in the declaration of the map. The
implementation of maps is such that access to the values is _very fast_.

Don’t confuse map X++ types with Map objects in AOT, which are used for
mapping tables with similar structures of fields
–

Set:

The functionality of Sets is similar to the list.  A Set is just an unordered list of items, while a list of items held by a Map
are indexed via a key.
Take look at
\Classes\sysLabel\LabelModuleId().