Type-check elimination: two object-oriented reengineering patterns

In reengineering an object-oriented system, we want to benefit from the expertise developed in earlier efforts. It is therefore essential to have a way to communicate expertise at different levels: from knowledge about how to approach a system to be reengineered, to knowledge about improving code by eliminating 'bad' style. In this paper, we propose to use a pattern form to communicate knowledge about reengineering. A reengineering pattern connects an observable problem in the code to a reengineering goal: it describes the process of going from the existing legacy solution causing or aggravating the problem to a new refactored solution which meets the reengineering goal. It thus gives a method which is appropriate for a specific problem, rather than proposing a general methodology, and makes reference to the appropriate tools or techniques for obtaining the refactored solution. In this paper, we discuss the role of reengineering patterns and contrast them with related kinds of patterns. We then highlight the form of reengineering patterns and present two simple patterns for type-check elimination.