CSC/ECE 517 Fall 2010/ch3 3d mr

Aspect-oriented programming and AspectR

AspectR is a very useful Ruby module, but it is not easy to find documentation on it that is appropriate for students taking this class. Find, or construct, documentation that explains what it does without presuming previous knowledge of AspectJ, that describes many or all methods of the module and how they work. Also find or produce an easy-to-understand example that does not involve logging. Show how the example would be implemented in AspectJ and AspectR.

AspectR

Defining Aspects and wrapping methods

AspectR provides a simple mechanism for wrapping methods in a program. One begins by creating a class that inherits from Aspect and defining the wrapper methods which will be called at the various join points in the program. AspectR currently supports only two method join points, PRE and POST. The inherited instance method =wrap= is then used to specify the target class and methods to intercept, along with the aspect methods to be called for the PRE and POST join points.

wrap takes the following parameters: ++ target - The target class ++ pre - Wrapper method to call before an intercepted method call ++ post - Wrapper method to call after an intercepted method call ++ *args -

• wrap (target, pre, post, *args) - method which allows you to wrap methods from the target class's pre and post methods

Other methods

• unwrap (AspectR::Aspect)

• add_advice (AspectR::Aspect)

• all_classes (AspectR)

• disable_advice_dispatching (AspectR::Aspect)

• dispatch? (AspectR::Aspect)

• get_methods (AspectR::Aspect)

• new (AspectR::Aspect)

• prepare (AspectR::Aspect)

• remove_advice (AspectR::Aspect)

• wrap_classes (AspectR)

• wrap_with_code (AspectR::Aspect)

• wrappable? (AspectR::Aspect)

Example

The code examples implement a code profiler to measure the duration of method calls.

AspectR

require aspectr.rb
include AspectR

class Profiler < Aspect
  def method_start(method, object, exitstatus, *args)
    @begin = Time.now
  end
  def method_end(method, object, exitstatus, *args)
    timeElapsed = Time.now - @begin
    puts "#{object.class}.#{method} took #{timeElapsed} secs"
  end
end

#if $0 == __FILE__
  class SomeClass
    def some_method
      puts "hello"
      sleep 5
    end
  end

  Profiler.new.wrap(SomeClass, :method_start, :method_end, /some/)
  SomeClass.new.some_method
#end