Type Object

By: R.E. Johnson, B. Woolf
Published in: PLoPD3
Pages: 47-65

Summary: Decouple instances from their classes so the classes can become instances of a class. Use two concrete classes, one whose instances represent the application's instances and one whose instances represent types. Each application instance has a pointer to its corresponding type.

• This pattern is similar to Strategy [Gamma+95] and State [Gamma+95]. All three break an object into pieces, and the real object delegates to the new object.
• An object may seem to be acting as Decorator [Gamma+95] for its Type Object. They have similar interfaces, but a Decorator does not behave like an instance of its Component.

Decouple instances from their classes so the classes can become instances of a class. Use two concrete classes, one whose instances represent the application's instances and one whose instances represent types. Each application instance has a pointer to its corresponding type.