From: badboy <badboy@...>
Date: 2009-02-07T04:17:06+09:00
Subject: Re: eval statement

Jonathan Wills schrieb:
> Trying to switch a project of mine from python to ruby.  Love ruby so
> far, but I'm finding that the eval statement is a bit more difficult to
> use than python's exec statement.  Here is one of the problems I'm
> having, RUBY_VERSION=1.9.1
> 
> a = 1
> eval('a=2')
> puts a
> 
> This will print out '2', as I want.  However if I remove the first line,
> 
> eval('a=2')
> puts a
> 
> r.rb:2:in `<main>': undefined local variable or method `a' for
> main:Object (NameError)
> 
> 
> Now if in the first case eval can change a variable in its scope, why
> can't it also create a variable in that same scope?  I may also not be
> totally clear on the way ruby handles scoping, which might be part of
> what I am having trouble understanding.
> 
> Any help understanding the eval statement would be appreciated.  I will
> probably have more questions about it, but I'll leave at this for now.
> 
> thanks,
> -Jonathan
why do you want to use eval?
eval is evil and in most cases not needed in Ruby