Using containers vs. other collection classes

I’ve seen containers used on some forms, so I thought this would be useful information.
This is based on my experience and some sites I’ve read (which I’ve given links to below).

If you’re going to store recIds as your datatype in any of these collection classes and you're not on AX 2012 yet, you should define the type like  this (because AX 2012 handles recIds differently, it will be easier for upgrading when you do this):

Declare a dictype variable like this:
DictType    dt = new DictType(extendedTypeNum(recid));

Then use it like this, here are examples for a map and a set:
msgMap = new Map(dt.baseType(),Types::String);

setRecIds = new Set(dt.baseType());

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 retrieved sequentially. This means that containers provide slower data access if you are working with a large numbers of records. You cannot modify a container in-place, instead each  addition or deletion has to iterate over the entire structure to copy all values into a newly allocated one. So every container manipulation has a run time of O(n). This is why they are not recommended to be used on forms. This site has some good information about how to use containers more efficiently when you do need to use them http://www.axaptapedia.com/index.php?title=Container If you are storing unique data of one type (like storing recids for a checkbox on a form),you can use a Set (see below). If you are storing non-unique data of the same type, use a List (see below).

Maps are most useful if you need a key for your data. I used a map recently to store the recId as a key to save/retrieve the inventTransId of some records. This is a good explanation of how to use Maps (http://www.axaptapedia.com/index.php?title=Map_Class)

Sets:
Sets are an unordered list of items. If you try to add something to a set that is already in the set, it will ignore it. Sets have an in() and remove() method which is useful. This is a good explanation of how to use Sets http://www.axaptapedia.com/index.php?title=Set_Class

Lists:
Lists contain elements that are accessed sequentially. Lists provide getEnumerator() and getIterator() methods (like sets do) which allow you to insert and delete items from the list. Here’s some information about Lists http://msdn.microsoft.com/en-us/library/aa848905%28v=ax.10%29.aspx.