From: Alexandru Popescu <the.mindstorm.mailinglist@...>
Date: 2005-09-14T20:07:48+09:00
Subject: Re: ruby and aop

Thanks for both suggestions so far. However these are easy solutions for the most commons things. 
When talking about aop there are a lot of joinpoints that are interesting, there are the intertype 
declarations (this part I think is pretty easy in Ruby), and maybe some more little tricks.

:alex |.::the_mindstorm::.|

#: Matthias Georgi changed the world a bit at a time by saying on  9/14/2005 12:11 PM :#
> 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
> 
> 
>