Technical Report Number
Advice in aspect-oriented programming helps programmers modularize crosscutting concerns by allowing additions and changes to a program's execution. However, formal reasoning about the functional behavior of aspect-oriented programs requires a non-modular, whole-program search to find applicable advice. To allow modular reasoning, we describe a discipline that categorizes aspects into two sorts: spectators and assistants. "Spectators" are statically checked to not modify the behavior of the code they advise; this restriction lets them remain unseen. Unlike spectators, "assistants" are not restricted in their behavior. However, for modular reasoning one must be able to identify all applicable assistants, hence assistants must be explicitly accepted by the code they advise. Besides allowing modular reasoning, this discipline permits the use of existing idioms, and appears to be statically verifiable and practical for software development. Indeed, expert aspect-oriented programmers seem to use such a discipline.