AspectOriented Software Development Karl Lieberherr Karl Lieberherr From

Aspect-Oriented Software Development Karl Lieberherr

Karl Lieberherr: From Doug Orleans’ Ph. D work Idea of branches • Each branch: – what to do – when to do it • Compare to a procedure – only says: what to do when a procedure with specific name is called. – a branch has control over when it will be called while a procedure has minimal control over when it is called

Karl Lieberherr: From Doug Orleans’ Ph. D work Idea of branches • Each branch: – what to do – when to do it • Compare to a method – only says: what to do when a method with specific name is called and the receiver has the right type. – a branch has control over when it will be called while a method has minimal control over when it is called

better separation of concerns may lead to less efficient compilation? Requirement on programming language • The degree of flexibility that the programming language allows in specifying the “when to do it” determines how well behavioral concerns can be separated. • By allowing a more precise specification of the “when to do it” part of a branch, we remove the tangling that would otherwise occur if the dispatch had to be implemented explicitly.

But • “when to do it” is very flexible: can do dangerous things? • Can influence an existing program in a way that is not desirable?

Design goals • Extensibility: It should be easy to add new functionality without editing code. • Refactorability: It should be easy to tease out existing functionality into something reusable: avoid duplication. • Parameterizability: It should be easy to reuse functionality in different contexts • Minimize duplication and tangling

Design goals • What is most important: reducing tangling. • If an incremental change is done through modification of existing code, it likely leads to tangling of concerns. • And crosscutting concerns lead to tangling too. • Is reducing code duplication a subcase of reducing tangling?

What is crosscutting? • One-to-many forward relationships and many-to-one inverse relationships. inverse one-to-many forward

Key idea of AOP • allow a module to define its trigger events so that one does not need to edit a large number of classes in order to program a crosscutting concern.

Modules • “what to do” – group several things to do together – what-module • “when to do it” – express several conditions together – when-module

Module examples • • • Aspect. J • DJ • BOP • AC • COOL • OOP Proc. Prog. • what advice visitor method b. branch body collaboration method managers method body procedure body • • • when pointcut strategy, cg visitor method s. branch condition adapter exclusion sets method signature procedure name