custom_aop.rb

require "rubygems"
require "active_support"

class CutPoint
  def self.monitor(monitored_klass)
    @local_instance = new()
    @monitored_klass = monitored_klass

    class << monitored_klass
      cattr_accessor :local_instance
    end
    @monitored_klass.local_instance = @local_instance
  end

  def self.before(options = {})
    methods = Array.wrap(options[:calls_to])

    intercept = options[:call]
    methods.each do |method_name|
      @monitored_klass.class_eval do
        alias_method "__original_cut__#{method_name}__", method_name
      end
      method_body =<<-EOF
        def #{method_name}(*args,&block)
          self.class.local_instance.#{intercept}(self,args)
          __original_cut__#{method_name}__(*args,&block)
        end
      EOF
      @monitored_klass.class_eval(method_body,__FILE__, __LINE__ + 1)
    end
  end

end


class Foo
  def hello(message)
    puts message.upcase
  end

  def my_name
    puts "Calling my name"
  end

  def wow
    name = yield
    puts "My name is #{name}"
  end
end

class Bleh < Foo
  def wow
  end
end

class FooPoint < CutPoint
  monitor Foo

  before(:calls_to => [:hello,:my_name,:wow], :call => :hello)

  def hello obj,args
    puts "Calling hello method"
  end
end

a = Bleh.new()

a.hello("Wow")
a.my_name()
a.wow { 'hemant' }