From: dblack@...
Date: 2006-03-04T12:59:25+09:00
Subject: Re: Write up on hazards of instance_eval?

Hi --

On Sat, 4 Mar 2006, itsme213 wrote:

> Is there any good write up on the hazards of instance_eval? Or do you happen
> to have your top-10 on the tip of your fingers?

I don't know whether there are ten distinct hazards, but a couple of
things to keep in mind:

instance_eval gives you more access to an object's state than the
object might have planned on.  You can change its instance variables
and call private methods, for example.

Another thing to be careful about is obscurity, caused by things like
this:

   class C
     def x(&block)
       @a = 1
       instance_eval &block
     end
   end

   @a = 2
   C.new.x { puts @a }   # 1, where a visual parse might suggest 2

Those are the things that come to mind, along with the usual eval
concerns in cases where you're giving instance_eval a string.


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

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