The ds_map data structure is an exceptionally useful one as it
lets you store key and value pairs. For example, a
character in your game can have a quantity of different items
(keys) and for each individual item he can have a number of
them (values), like in an RPG where you can have 10 health
potions, 5 mana potions and 100 gold. Maps maintain such pairs all
together in the one place and you can add pairs to the map and
search for the value corresponding to certain keys as well using
some simple functions. There are a couple of things you should know
about maps before you use them, however! Maps are not sorted
in any (recognisable) way, meaning that to find a certain key you
may have to iterate through the whole thing (which is very
slow). There is also no way to hold two keys that are the same, nor
can you assign one key two values.
NOTE: The ds_map functions have changed since previous versions of GameMaker so imported games may not work or behave as you expect.
NOTE: As with all dynamic resources, data structures take up memory and so should always be destroyed when no longer needed to prevent memory leaks which will slow down and eventually crash your game.
The following functions exist that deal with DS maps.
There are four further functions available for saving and loading a ds_map. These functions will encrypt the map and store it in a secure location on the target platform, so you can use this to save In App Purchase details, passwords, sensitive game information, etc...
Apart from these specific functions you can all use an expression (called an accessor) to add or modify the contents of your ds_map. This accessor looks similar to a 1D array with the following syntax:
You can find more information, plus examples, from from the GML
Overview page on Accessors.
One of the uses that ds_maps have is when working with JSON, and so there are a few special functions that are specific to that:
There are also a couple of complimentary functions for ds_lists:
NOTE: While these functions permit you to add lists
and maps within a map, they are useless for anything other than
JSON, and nested maps and lists will not be read correctly if
written to disk or accessed in any other way.
NOTE: if you need to check if a data structure exists, you can use the ds_exists() function.