From: Matthias Georgi <matti.georgi@...>
Date: 2005-09-14T19:11:39+09:00
Subject: Re: ruby and aop

Hi Alexandru!

I think, aop-like programming is done mostly by redefining methods.
This is somewhat ugly, as you have to alias the old method.
A good example is the once macro as used in freeride or date.rb:

module Once
  def once(*ids)
    for id in ids
      module_eval <<-"end;"
        alias_method :__#{id.to_i}__, :#{id.to_s}
        private :__#{id.to_i}__
        def #{id.to_s}(*args, &block)
          (@__#{id.to_i}__ ||= [__#{id.to_i}__(*args, &block)])[0]
	end
      end;
    end
  end
  private :once
end

By using once, you can cache method results like:

class MyClass
  extend Once
  once :my_method
end

I can imagine a cleaner aop-style of doing this like:

aspect_around MyModule::MyClass, :my_method do |meth, *args|
  ( @__my_method__ ||= [ meth.call(*args) ] )[0]
end

or more generally

module Once
  def once(*ids)
    for id in ids
      aspect_around self, id do |meth, *args|
        if cache = instance_variable_get("@__#{id}__")
          cache[0]
        else
          result = meth.call(*args)
          instance_variable_set("@__#{id}__", [result])
        end
      end
    end
  end
end