From: "John W. Long" <ng@...>
Date: 2006-07-22T12:10:54+09:00
Subject: Re: [ANN] Mongoose 0.2.0

Jamey Cribbs wrote:
> The way it works is that in the Plane.find method, I grab the block and 
> pass it to #instance_eval.  This executes the block in the Plane classes 
> environment, so it knows that when it sees the attribute "speed" or 
> "country" in the block, it knows to call Plane.speed and Plane.country.  
> Planes.speed happens to be a reference to a SkiplistColumn instance and 
> it knows how to handle the "> 350" passed to it.

The problem with this approach is that you loose access to instance 
variables. For instance:

   >> class Object
   >>   def with(&block)
   >>     instance_eval(&block)
   >>   end
   >> end
   => nil
   >> @test = 1
   => 1
   >> Object.new.with { puts @test }
   => nil

In the above example @test when used within the context of the with 
block is thought to be an instance variable of the object, which is why 
it returns nil instead of 1. I consider this behavior undesirable.

--
John Long
http://wiseheartdesign.com