Metaobject
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In computer science, a metaobject or meta-object is any entity that exhibits aspects of an object, such as the object's type, interface, class, methods, attributes, variables, functions, control structures, etc.
A meta-object protocol (MOP) is a generalized way to handle a group of objects as whole. This can be useful in implementing generic functions. It may manifest as a set of classes and methods that allow a program to inspect the state of the supporting system and alter its behaviour.
Possibly the best-known MOP is the one described in the book "The Art of the Metaobject Protocol"; it applies to the Common Lisp Object System and allows the mechanisms of inheritance, method dispatch, class instantiation and so on to be manipulated.
In the case of multiple inheritance, there is the question how conflicting slots and methods of the superclasses are to be resolved. The language designers typically select one solution, and the language users must live with it. A meta-object protocol, on the other hand, makes it possible to change the rules of inheritance and choose a different solution for individual classes.
A metaobject protocol is one way to implement aspect-oriented programming languages. Many of the early founders of MOPs, including Gregor Kiczales have since moved on to be the primary advocates for aspect-oriented programming.
External links
- The guile MOP specification (tiny clos) (http://www.gnu.org/software/guile/docs/goops/MOP-Specification.html#MOP%20Specification)
References
- Gregor Kiczales, Jim Des Rivieres, Daniel G. Bobrow: The Art of the Metaobject Protocol, MIT Press, ISBN 0262111586 or ISBN 0262610744
See also:
References
- Definitions of metaobject (http://www.google.com/search?q=define:metaobject)
- Metaobjects and the Metaobject Protocol (http://www.gnu.org/software/guile/docs/goops/Metaobjects-and-the-Metaobject-Protocol.html)