From: Trans <transfire@...>
Date: 2008-03-15T07:23:51+09:00
Subject: Re: Transparent Lazy execution



On Mar 14, 2:59 pm, Eric Anderson <e...@pixelwareinc.com> wrote:
> I have often wanted to execute a bit of code only if the result of
> that code is used later. For example in a Rails app I might load some
> data in my controller but sometimes depending on some situations the
> result is not actually used in the view.
>
> So what I want is to be able to do:
>
> @recent = lazy { Post.find_recent 5 }
>
> But then if @recent is never used the actual search is not executed.
> But because I don't want to break compatibility once @recent is used I
> want it to act and behave exactly like it is the return value of the
> block. Even the core methods like class and respond_to? should return
> the correct values.
>
> So I took my first stab at it. You can see it at:
>
> http://files.pixelwareinc.com/transparent_lazy.rb
>
> My questions are:
>
> 1. What trouble am I getting myself into by allowing this object to
> completely loose it's identity?
> 2. What holes are in the armor? Is there any way my proxy class does
> not act like the result of the block? If there are, do they matter?
> 3. What are the performance and memory implications?
>
> The only hole I can think of is that you see the proxy if you are
> stepping through your code. This is no big deal to me.
>
> There would be a slight memory increase as there is an extra object
> but it should be insignificant. And everything should be garbage
> collected when nothing is using the proxy object anymore so I don't
> forsee any memory leaks. Obviously every call to the lazy-loaded data
> incurs an extra method call but I think I can live with that.
>
> My next step will be to monkey-patch this into Rails so that
> ActiveRecord::Base.find will use the lazy method by default. This will
> allow everything to be lazy loaded without having to change a single
> line of code in my application.

Have you looked at lazy.rb?

T.