From: Dave Burt <dave@...>
Date: 2006-01-25T00:58:51+09:00
Subject: Re: LazyLoad

Erik Veenstra wrote:
> ...
> Comments? Ideas? Something I overlooked?
> ...
> class LazyLoad
>   def initialize(object, load_method, property)
>     @object            = object
>     @property          = property
>     @load_method       = load_method
>   end
>
>   def method_missing(method_name, *parms, &block)
>     @object.send(@load_method)
>     @object.instance_eval("@#{@property.to_s}").send(method_name,
> *parms, &block)
>   end
> end

Interesting. Here's a potential problem. You won't hit method_missing for 
methods that Object has. In particular, a client might use dup, ==, to_s, 
class, kind_of?, and so on. You might try getting around some of this by 
using Delegate from the standard library, or Facets' BlankSlate IIRC.

I was thinking three parameters was too many for LazyLoad#initialize (just 
provide a block which loads and returns the loaded value), and started to 
rewrite it, when I remembered MenTaLguY's lazy.rb, which does something very 
similar.

STEP 4, INTRODUCING lazy.rb

 class Branch
   def initialize
     @items = promise do
       @items = {}
       # Fill @items... EXPENSIVE, TIME CONSUMING, MEMORY HUNGRY!
       @items
     end
   end
 end

Cheers,
Dave