From: Jacob Fugal <lukfugl@...>
Date: 2006-06-24T00:52:48+09:00
Subject: Re: How odd is Ruby code allowed to be?

On 6/22/06, dblack@wobblini.net <dblack@wobblini.net> wrote:
> Why not:
>
>    aspect = Aspect.new do |a|
>      a.apply_to_types SomeClass, String, FooBar
>      a.pointcut("some_method",...).with(LoggingInterceptor.new)
>      a.register_with_aop_engine
>    end

Like others, I'm not sure how the implementation of the
apply_to_types, pointcut and register_with_aop_engine will go (I'm
sure there's some... I'm just not worrying about it), but I agree with
David that an instance of the Aspect class is probably what you really
want. I'd clean the syntax up ("clean" being just my opinion) a little
more like:

  aspect(SomeClass, String, FooBar) do
    pointcut :some_method,
      :some_prop=,
      :some_prop,
      :length
    with LoggingInterceptor.new
  end

Implementation of the builder:

  def aspect(*classes, &definition)
    AspectBuilder.instance.build(*classes, &definition)
  end

  class AspectBuilder
    include Singleton

    def build(*classes, &definition)
      @aspect = Aspect.new
      @methods = []
      @aspect.apply_to_types *classes
      instance_eval &definition
      @aspect.register_with_aop_engine
    end

    def pointcut(*methods)
      @methods += methods
    end

    def with(interceptor)
      @aspect.pointcut(*@methods).with(interceptor)
      @methods = []
    end
  end

Sample implementation of the Aspect class (just stubbing here):

  class Aspect
    def apply_to_types(*classes)
      @classes = classes
    end

    def pointcut(*methods)
      cut = PointCut.new(*methods)
      (@cuts ||= []) << cut
      cut
    end

    def register_with_aop_engine
      classes = @classes.size == 1 ? @classes[0] :
        [@classes[0..-2].join(', '), @classes[-1]].join(' and ')

      puts "Adding an aspect on #{classes} with the following cuts:"
      @cuts.each{ |cut| puts "\t#{cut}" }
    end

    class PointCut
      def initialize(*methods)
        @methods = methods
      end

      def with(interceptor)
        @interceptor = interceptor
      end

      def to_s
        methods = @methods.size == 1 ? @methods[0] :
          [@methods[0..-2].join(', '), @methods[-1]].join(' and ')

        "Cutting #{methods} with a #{@interceptor.class}"
      end
    end
  end

Output of the above built aspect with the Aspect stub as above and
simple classes for SomeClass, FooBar and LoggingInterceptor:

  Adding an aspect on SomeClass, String and FooBar with the following cuts:
        Cutting some_method, some_prop=, some_prop and length with a
LoggingInterceptor

Jacob Fugal