The Art of Assembly Language, 2nd Edition

12.12 Abstract Methods

An abstract base class is one that exists solely to supply a set of common fields to its derived classes. You never declare variables whose type is an abstract base class; you always use one of the derived classes. The purpose of an abstract base class is to provide a template for creating other classes, nothing more. As it turns out, the only difference in syntax between a standard base class and an abstract base class is the presence of at least one abstract method declaration. An abstract method is a special method that does not have an actual implementation in the abstract base class. Any attempt to call that method will raise an exception. If you're wondering what possible good an abstract method could be, keep on reading. ...