Aspect-Oriented Programming: An Overview Brandon Wirick Feb. 2005

1. Aspect-Oriented Programming: An Overview Brandon Wirick Feb. 2005

2. Layers of Abstraction • Machine code to assembly • Assembly to procedural languages • Procedural to object-oriented • Group similar compile-time functional units • Object- to aspect-oriented • Group similar run-time functional units

3. Join-point Poincut Weaving compile-time run-time Loop fusion Tangling Terminology • AOP • AOSD • Concerns • common • crosscutting • Aspect • AspectJ

4. AspectJ • Java with aspects • Aspects are singleton classes • Group join-points into pointcuts • Define behavior before, after, or around pointcuts • Specify contract enforcements • Can contain members, like classes • Definitely most prominent language

5. AspectJ Example public aspect NoNulls { public static interface Addable { public boolean add(Object o); } pointcut add(Object o) : call(boolean Addable.add(Object)) && args(o); boolean around(Object o) : add(o){ boolean success = (o != null); success &= proceed(o); return success; } } class NoNullsVector extends Vector implements NoNulls.Addable {} class NoNullsArrayList extends ArrayList implements NoNulls.Addable {}

6. Kiczales et al, 1997 • Noted certain problems could have implementations that are either • Efficient, but hard to understand • Inefficient, but easy to understand • Efficient and easy to understand, but only with AOP! • “Reduction in bloat due to tangling”

7. Design Pattern Libraries public abstract aspect ObserverProtocol { protected interface Subject {} protected interface Observer {} ... protected abstract pointcut subjectChange(Subject s); ... public aspect ColorObserver extends ObserverProtocol{ declare parents: Point implements Subject; declare parents: Screen implements Observer; ...

8. Not for Dumb Programmers • Easy to do wrong • Complicated to understand • Controversial • Not so much anymore • Arguments against AOP pretty weak • Some unpredictable behavior?