Editing Metaobject (section)

=== Usage ===
The first metaobject protocol was in the [[Smalltalk]] object-oriented programming language developed at [[Xerox PARC]]. The [[Common Lisp Object System]] (CLOS) came later and was influenced by the Smalltalk protocol as well as by [[Brian Cantwell Smith|Brian C. Smith]]'s original studies on 3-Lisp as an infinite tower of evaluators.<ref>{{cite book |pages=298–307 |author1=Daniel P. Friedman |author2=Mitchell Wand |title=Proceedings of the 1986 ACM conference on LISP and functional programming - LFP '86 |chapter=The mystery of the tower revealed: A non-reflective description of the reflective tower |date=1988 |doi=10.1145/319838.319871 |isbn=978-0897912006 |s2cid=7974739 }}</ref> The CLOS model, unlike the Smalltalk model, allows a class to have [[Multiple inheritance|more than one superclass]]; this raises additional complexity in issues such as resolving the lineage of the class hierarchy on some object instance. CLOS also allows for [[multiple dispatch|dynamic multimethod dispatch]], which is handled via [[generic functions]] rather than [[message passing]] like in Smalltalk's [[single dispatch]].<ref>{{cite web|title=Integrating Object-Oriented and Functional Programming|url=https://www.cip.ifi.lmu.de/~langeh/test/2004%20-%20Gabriel%20-%20CLOS%20-%20Integrating%20Object-Oriented%20and%20Functional%20Programming.pdf|access-date=7 July 2016}}</ref> The most influential book describing the semantics and implementation of the metaobject protocol in Common Lisp is ''[[The Art of the Metaobject Protocol]]'' by [[Gregor Kiczales]] et al.<ref>{{cite book|last=Kiczales|first=Gregor|title=The Art of the Metaobject Protocol|publisher=The MIT Press|isbn=978-0262610742|author2=Jim des Rivieres |author3=Daniel G. Bobrow |date=July 30, 1991}}</ref>

Metaobject protocols are also extensively used in software engineering applications. In virtually all commercial CASE, re-engineering, and Integrated Development Environments there is some form of metaobject protocol to represent and manipulate the design artifacts.<ref>{{cite journal|last=Johnson|first=Lewis|author2=David R. Harris |author3=Kevin M. Benner |author4=Martin S. Feather |title=Aries: The Requirements/Specification Facet for KBSA|journal=Rome Laboratory Final Technical Report|date=October 1992|volume=RL-TR-92-248}}</ref><ref>{{cite web|title=The Origin of Refine|url=http://www.metaware.fr/images/pdf/1_Metaware_The_Origin%20of_Refine_Whitepaper.pdf|work=www.metaware.fr|publisher=Metaware White Paper|access-date=6 January 2014|url-status=dead|archive-url=https://web.archive.org/web/20140107000613/http://www.metaware.fr/images/pdf/1_Metaware_The_Origin%20of_Refine_Whitepaper.pdf|archive-date=7 January 2014}}</ref><ref>{{cite web|title=OMG's MetaObject Facility|url=http://www.omg.org/mof/|work=omg.org|publisher=Object Management Group|access-date=7 January 2014}}</ref>

A metaobject protocol is one way to implement [[aspect-oriented programming]]. Many of the early founders of MOPs, including [[Gregor Kiczales]], have since moved on to be the primary advocates for aspect-oriented programming. Kiczales et al. of [[Palo Alto Research Center|PARC]] were hired to design [[AspectJ]] for [[Java (programming language)|Java]], a language which does not possess a native metaobject protocol.