From: Joel VanderWerf <vjoel@...>
Date: 2005-10-10T06:31:00+09:00
Subject: Re: using lambda/Proc can prevent a lot of garbage collection

Eric Hodel wrote:

> A closure should only enclose the variables needed for its execution. 
> This is actually not very difficult but unfortunately eval('a') prevents
> Ruby from excluding unbound variables in closures.
> 
> This is a (unfortunate IMO) feature of Ruby.
> 

Aren't there some useful hacks that depend on being able to get at vars
in the caller's scope (which need not be referenced in the block), using
 the

  eval str, some_proc

construct?

I use it in my observable lib to get the self of the block's context,
using something like this:

      def when_#{var} pattern=Object, &block
        observer_map = @#{var}__observer_map ||= ObserverMap.new
        if block
          observer = eval "self", block

to find out what object is observing a variable. But that's not as
objectionable as getting access to arbitrary local vars in that context.

Does anyone remember--is there is anything that uses the latter kind of
access (arb. local vars) that is more than just a cute hack? Is there
anything really useful we would lose without that behavior?

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407