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GUI for .NET Primer
Object-oriented Programming in ABL : Garbage collection

Garbage collection

ABL developers are familiar with the use of the DELETE OBJECT statement for destroying handle-based objects, such as a widget, a procedure, a server, or a socket. Explicitly deleting class-based objects is not necessary because of garbage collection. Class-based objects are deleted during garbage collection when all references to that object have been removed, that is, when its reference count goes to zero.
As long as you need an object, you must ensure that you maintain an object reference to that object. You can always assign the object reference to another variable before it goes out of scope, or you can pass it to another procedure, where you can continue to manage the object until either you delete it or it is deleted by garbage collection.
Garbage collection does not delete a class-based object with a circular reference. For example, Object A has a reference to Object B and Object B has a reference to Object A. To delete an object with a circular reference you must use the DELETE OBJECT statement.