Release 10.1A: OpenEdge Getting Started:
Object-oriented Programming

Supporting 4GL

The following 4GL elements specially support programming of and programming with class-based objects:

SUPER statement — Invokes the constructor of the immediate super class from the constructor of the invoking subclass. For more information, see the "Constructing an object" section.
SUPER system reference — Invokes the implementation of a specified method within a class hierarchy as implemented in the lowest super class above the invoking subclass. Analogous to the RUN SUPER statement or SUPER function in procedure-based programming. For more information, see the "Calling a super class method" section.
CAST function — Allows a super class object reference to be assigned to a related subclass object reference. For more information, see the "Assignment and the CAST function" section.
TYPE-OF function — Verifies the type of an object. For more information, see the "TYPE-OF function" section.
VALID-OBJECT function — Validates that an object reference points to a real object. Analogous to the VALID-HANDLE function for internal object handles. For more information, see the "VALID-OBJECT function" section.
THIS-OBJECT system reference — Returns an object reference to the current object from a method within the class hierarchy of the object. Analogous to the THIS-PROCEDURE object handle for procedures. For more information, see the "THIS-OBJECT system reference" section.
FIRST-OBJECT attribute — A SESSION handle attribute that returns an object reference to the first class-based object instantiated in a Progress session. Analogous to the FIRST-PROCEDURE attribute for persistent procedures. You can use the NEXT-OBJECT data member of any class to walk the list of instantiated class-based objects forward from the first to the most recent object currently instantiated in the session. All user-defined classes inherit NEXT-OBJECT from the root class, Progress.Lang.Object. For more information on the FIRST-OBJECT attribute and the NEXT-OBJECT data member, see the "Progress session object references" section.
LAST-OBJECT attribute — A SESSION handle attribute that returns an object reference to the most recent class-based object instantiated in a Progress session. Analogous to the LAST-PROCEDURE attribute for persistent procedures. You can use the PREV-OBJECT data member of any class to walk the list of instantiated class-based objects backward from the most recent to the first object currently instantiated in the session. All user-defined classes inherit PREV-OBJECT from the root class, Progress.Lang.Object. For more information on the LAST-OBJECT attribute and the PREV-OBJECT data member, see the "Progress session object references" section.