REFLECTIONS ON METAPROGRAMMING

By encapsulating aspects of language semantics within a set of default classes and allowing the programmer to derive new versions, object-or iented languages whose semantics can be tailored to the needs of indiv idual programmers have been provided, The degree to which such languag es are simultaneously flexible and efficient is an open question, We d escribe our experience with using this technique to incorporate transp arent support for persistence into the Common Lisp Object System via i ts' metaobject protocol, an open implementation based on reflection, F or many aspects of our implementation the metaobject protocol was perf ectly suitable, In other cases we had to choose among extending the pr otocol, requiring the application programmer to employ special idioms, and tolerating a large performance penalty. Based on our experience w e evaluate the metaobject protocol, propose some improvements and exte nsions, and present performance measurements that reveal the need for improved language implementation techniques.