1. One or more tangible non-transitory computer-readable storage media for storing computer-executable instructions executable by processing logic, the media storing one or more instructions for: defining by the computer a first class as a subclass of a superclass in the programming environment, wherein the subclass and the first class are handle classes; defining by the computer a second class and a third class as non-handle classes in the programming environment; preventing by the computer defining a subclass of the handle first class and the non-handle second class based on the first class being a handle class and the second class being a non-handle class in the programming environment; defining by the computer a class attribute that identifies combinable classes; identifying by the computer the non-handle third class as combinable with handle classes in the programming environment based on the class attribute; and defining by the computer a subclass of the non-handle third class and the handle first class in the programming environment, wherein the non-handle third class and the handle first class are combinable based on the class attribute.