From: Robert Dober <robert.dober@...>
Date: 2007-07-01T19:27:20+09:00
Subject: Re: Newbie Question. eval.rb variable scope issue

On 7/1/07, Rishel,Wes <Wes.Rishel@gartner.com> wrote:
> I am a Python duffer who got interested in Rails an decided to check out
> Ruby.

Welcome to the jewel.
Local variables spring into existance in the scope they are assigned to
Our friend irb shows this quite nicely

irb(main):008:0> %w{ word=2 word }.each{|c| p eval( c )}
2
NameError: undefined local variable or method `word' for main:Object
        from (irb):8
        from (irb):8:in `eval'
        from (irb):8
        from (irb):8:in `each'
        from (irb):8
        from :0
irb(main):009:0> word=nil
=> nil
irb(main):010:0> %w{ word=2 word }.each{|c| p eval( c )}
2
2
=> ["word=2", "word"]

eval creates a scope of it's own, thus eval("word=2") brings it into
life and it sadly dies.
But when eval("word=2") assigns to the already existing local variable
in the outer scope it persists into the next eval.

And just a friendly hint, forget eval you *do not need it* :).

HTH
Robert

-- 
I always knew that one day Smalltalk would replace Java.
I just didn't know it would be called Ruby
-- Kent Beck