Software Engineering Lecture 7 Vladimir Safonov, Professor, head of laboratory St. Petersburg University Email: v_o_safonov@mail.ru WWW: http://user.rol.ru/~vsafonov Язык программирования Java. Лекция 1

Aspect-oriented programming (AOP): Aspect Aspect – an implementation of a crosscutting concern Aspect – special kind of a module to be used by its weaving into other modules Examples of aspects: - implementation of MT safety for an existing library - implementation of a new source language feature in a compiler So aspects are ubiquitous in programming, but still added and located “by hand”, hence the modularity and maintenance issues (C) Vladimir O. Safonov, 2004

The structure of aspect definition (V. Safonov) Aspect name Aspect parameters (optional) – generic aspects desirable Aspect data Aspect modules Aspect actions, with their weaving rules A separate reusable sets of weaving rules possible, to be used when weaving different aspects (C) Vladimir O. Safonov, 2004

Aspects – static or dynamic? First view on aspects: Aspect weaving is a kind of “tangled macro expansion”: Second view: Aspect weaving is performed dynamically, at runtime if Condition then Action (looks like debugging breakpoints – well know for years) Our viewpoint (V. Safonov): we take the static view but do recognize the dynamic view should be also implemented (C) Vladimir O. Safonov, 2004

Aspects in AspectJ (1/2) AspectJ: Xerox PARC (1995) -> Univ. of British Columbia, Canada (2003), designed by prof. Gregor Kichales AspectJ – aspect-oriented extension of Java (compiler from the extended language, debugger in terms of aspects, Aspect GUI) Pointcut – definition of a group of weaving rules ( using wildcards for entity names), - not tied to a concrete code Join points – concrete points in concrete code to be modified in aspect weaving Advices – actions to be performed at join points (C) Vladimir O. Safonov, 2004

Aspects in AspectJ (2/2) Aspects in AspectJ are essentially dynamic (similar to debugging-style breakpoints/debugging actions) Introduce – weaving new definitions into a module; these definitions are visible by the aspect only (no encapsulation violation happens) around S A -> B - AspectJ style of code modification at runtime (self-modifying code); actually, AspectJ behaves as term rewriting system. Our viewpoint: this is a powerful tool but potentially dangerous (C) Vladimir O. Safonov, 2004

Aspects in Aspect.NET (V. Safonov) Static approach to AOP very important: it improves program readability Aspects for .NET should be cross-language Using custom attributes (AspectDef, AspectRef) Syntactic sugar: a simple AOP annotations meta-language converted to AOP attributes Aspectizing (classical term – aspect mining): turning non-AOP programs into AOP ones (coloring the aspects) Aspect GUI Aspect.NET site: http://aspect-dot-net.sscli.net (C) Vladimir O. Safonov, 2004

Other new programming paradigms Logic programming Functional programming Event-driven programming Generic programming Meta-programming (C) Vladimir O. Safonov, 2004

Home task and references to lecture 7 http://aosd.net - the main Web site on AOP http://aspectj.org - the AspectJ Web site Safonov V. O. Aspect.NET – a new approach to aspect-oriented programming. – In: “.NET Developer’s Journal”, 2003, # 4. (C) Vladimir O. Safonov, 2004