AspectR - Simple aspect-oriented programming in Ruby

Version:          0.4.0
Release date:     2006-11-11
Home page:        http://aspectr.sf.net/
Tarball:          http://prdownloads.sf.net/aspectr/aspectr-0-3-5.tar.gz
Authors:          Avi Bryant and Robert Feldt
Email:            avi@beta4.com, feldt@ce.chalmers.se
Contributors:     Guy Builta, Robert Herbig, Mark Karasek

What is it?

Aspect-oriented programming concepts to Ruby. Essentially it allows you to wrap code around existing methods in your classes. This can be a good thing (and even affect how you design your code) since it separates different concerns into different parts of the code. It is somewhat similar to AspectJ, www.aspectj.org.

Main features of AspectR (in AspectJ lingo): * Join points:

object receives method/constructor call, and
field accessed (if access is via getter/setter method) * Advices: before (pre), after returning and after throwing (post), around * Aspects: classes inheriting Aspect.
supports "abstract" Aspects and overriding between advices. * Wildcards (really regexps) can be used in pointcut designators, ie. to specify classes and methods to wrap advice's to. * Pointcut parameters. Advices can access:
object and method receiving call,
arguments to call,
return values, and
exceptions raised. * Predicated execution of advice. Eg: a predicate can be given when advice is attached to a method(s).

Installation?

unpack tarball (if you haven't already)
install: ruby install.rb
If you've got RubyUnit you can also run tests: ruby tests/runtests.rb

Example of use?

See tests, try out any of the files in examples/ or check out the aspects in the aspects subdir.

Documentation?

AspectR lets a module wrap any number of methods in other classes (or objects) with the "advice" methods (in the lingo of Aspect/J) of the module.

Usage:

require 'aspectr'
include AspectR
class MyAspect < Aspect
  def someAdviceMethod(method, object, exitstatus, *args)
    ...
  end
  ... some other advice methods ...
end
ma = MyAspect.new
ma.wrap(someClassorObject, :preAdvice, :postAdvice, ... methods to wrap...)
or
ma.wrap(someClassorObject, :preAdvice, :postAdvice, /patternToWrap/)
or
AspectR.wrap_classes(ma, :preAdvice, :postAdvice, [Class1, Class2], ...methods to wrap...)

Advice methods are passed a variable number of parameters: the first is the name of the method currently being wrapped the second is the object receiving the method call the third is the exit/return status:

        Array with return value(s) if the method exited normally
        true if the method exited with an exception
        nil if the method hasn't yet exited (for preAdvice)

the rest are the arguments that were passed to the wrapped method.

I'm confused by the different version of this? What is/was 'advice.rb'?

AspectR was originally called advice.rb and written by Avi Bryant. Later Robert Feldt changed/tweaked/extended it. Avi then refactored very nicely, Robert tweaked a bit more and on it goes... ;-) In late 2006, three students from Rose-Hulman Institute of Technology, www.rose-hulman.edu, updated AspectR to include several new features. For details see CHANGELOG.

Join points: method/constructor called, method/constructor executes (?), exception handler executes
Most of the pointcut designator primitives
Composition of pointcut designators (well you can of course specify several method calls in different classes and objects)
precedence/specificity among advices/aspects
reflection by sending joinpoint object to advices with context of join point etc (easily added but why?)
control-flow based crosscutting (might be possible if we locally attach a trace func but are they needed?)

Do you have comments or questions?

We'd appreciate if you drop us a note if you're using AspectR. If there are some known users we'll be more motivated to pack up additions / new versions and post them to RAA.

Happy coding!

Avi and Robert Feldt