Traces (A Cut at the "Make Isn't Generic" Problem)

Object-oriented techniques are a powerful tool for making a system end-programmer specializable. But, in cases where the system not only accepts objects as input, but also creates objects internally, specialization has been more difficult. This has been referred to as the "make isn't generic problem." We present a new objectoriented language concept, called traces, that we have used successfully to support specialization in cases that were previously cumbersome. The concept of traces makes a fundamental separation between two kinds of inheritance in object-oriented languages: inheritance of default implementation -- an aspect of code sharing; and inheritance of specialization, a sometimes static, sometimes dynamic phenomenon. The Problem Object-oriented programming languages have proven to be a powerful tool for making a variety of systems end programmer specializable [KL92]. That is, once the system has been written, compiled and distributed, another programmer can modify or extend i..