Subclassing Opaque Types

If you create a subclass of a partially revealed superclass, all of the superclass methods are still in your interface, even if they were hidden to you. For example, suppose there another interface to Directory that reveals some more of Directory.T, as illustrated below. Given that interface, a malicious user could do the following:

IMPORT Directory, DirectoryFriend, FileSystemDirectory;

NARROW(NEW(FileSystemDirectory.T), Directory.T).oops();

Last changed July 17, 1996

whsieh@cs.washington.edu