Pluggable Aspect Instantiation Models

An aspect encapsulates not only a crosscutting behavior, but also a crosscutting state. When aspects are stateful, there is a need to specify and control their instantiation. Unfortunately, aspect instantiation is a hard-wired feature in AspectJ. This feature cannot be customized by the application programmer. Speci cally, there are six pre-de ned instantiation models to choose from, each designated by a keyword: issingleton, perthis, pertarget, perc ow, perc owbelow, pertypewithin. In this work, we introduce a new language mechanism and keyword `perscope' that lets third-parties de ne custom aspect instantiation models. This new keyword replaces the six existing keywords in AspectJ, and may eliminate the need for introducing future ones.