Using Guard Predicates for Generalized Control of Aspect Instantiation and Activation
Stephan Herrmann, Christine Hundt, Katharina Mehner, Jan Wloka · 2005
Many aspect-oriented programming languages employ static transformations in order to produce the executable system. Some aspects, however, should only be effective if certain conditions are fulfilled that can only be evaluated at runtime. The naïve approach of using conditionals within the advice code easily leads to scattering and tangling regarding these conditionals, suggesting that they should be separated from the advice code. In this paper we analyze how aspects can be made conditional, i.e. how their effect can be controlled based on runtime values. We present an extension to the ObjectTeams/Java programming language that provides a flexible means for controlling the instantiation and activation of an aspect implemented by a ”team ” and its roles by means of guard predicates. We discuss different points in a program for which we consider a guard predicate suitable. We argue that this approach is more general than the ways other aspect languages control aspect instantiation and activation. Our approach makes use of the fact that in Object Teams aspects are implemented as first-class objects, which have full support for inheritance and polymorphism. 1.