Reference counting as memory management has a drawback in that it is difficult to detect circular references when determining dead objects. AngelScript allows the application to register types with special behaviours to support the garbage collection for detecting circular references. These behaviours make the class a bit more complex, but you should only have to register them for a few types, e.g. generic container classes.
The difference between the garbage collected and non-garbage collected types is in the addref and release behaviours, the class constructor, and the extra support behaviours.
The GC determines when objects should be destroyed by counting the references it can follow for each object. If the GC can see all references that points to an object, it knows that the object is part of a circular reference. If all the objects involved in that circular reference have no outside references it means that they should be destroyed.
The process of determining the dead objects uses the first for of the behaviours below, while the destruction of the objects is done by forcing the release of the object's references.
Whenever a garbage collected class is created, the garbage collector must be notified of it's existence. The easiest way of doing that is to have the factory behaviour, or the class constructor call the
NotifyGarbageCollectorOfNewObject() method on the engine when initializing the class.
You may want to consider caching the typeId, so that it doesn't have to be looked up through the relatively expensive call to GetTypeIdByDecl every time an object of this type is created.
Note, if you create objects of this type from the application side, you must also notify the garbage collector of its existence, so it's a good idea to make sure all code use the same way of creating objects of this type.
For garbage collected objects it is important to make sure the AddRef and Release behaviours clear the GC flag. Otherwise it is possible that the GC incorrectly determine that the object should be destroyed.