The Art of the Metaobject Protocol

The CLOS metaobject protocol is an elegant, high-performance extension tothe CommonLisp Object System. The authors, who developed the metaobject protocol andwho were among the group that developed CLOS, introduce this new approach toprogramming language design, describe its evolution and design principles, andpresent a formal specification of a metaobject protocol for CLOS.Kiczales, desRivi?res, and Bobrow show that the "art of metaobject protocol design" lies increating a synthetic combination of object-oriented and reflective techniques thatcan be applied under existing software engineering considerations to yield a newapproach to programming language design that meets a broad set of designcriteria.One of the major benefits of including the metaobject protocol inprogramming languages is that it allows users to adjust the language to better suittheir needs. Metaobject protocols also disprove the adage that adding moreflexibility to a programming language reduces its performance. In presenting theprinciples of metaobject protocols, the authors work with actual code for asimplified implementation of CLOS and its metaobject protocol, providing anopportunity for the reader to gain hands-on experience with the design process. Theyalso include a number of exercises that address important concerns and openissues.Gregor Kiczales and Jim des Rivi?res, are Members of the Research Staff, andDaniel Bobrow is a Research Fellow, in the System Sciences Laboratory at Xerox PaloAlto Research Center.