From: Ryan <rdonahue@...>
Date: 2010-09-25T13:00:14+09:00
Subject: Re: Using the same variable for an array and an iterator

On Sep 24, 10:55 pm, Michael Fellinger <m.fellin...@gmail.com> wrote:
> On Sat, Sep 25, 2010 at 11:30 AM, Ryan <rdona...@gmail.com> wrote:
> > I've just started learning Ruby and am going through a few tutorials.
> > Right now I'm playing around with arrays and am getting a strange
> > error.  I am creating an array named 'x' and creating an iterator
> > named x as well.  Now I know that this isn't good practice but I'm
> > getting a strange error.  The first time I iterate through the entire
> > array, simply displaying the contents of the array, I don't get an
> > error at all.  If I immediately run the iteration again I get a
> > NoMethodError and am trying to figure out why.  Here's a screenshot
> >http://bit.ly/bXZkjp
> > Like I said, I know that this is bad practice, but I'm curious as to
> > what is causing this error only after the first go through.
>
> Ruby 1.8 doesn't shadow local variables used as block arguments.
> That means what happens is that x is assigned the current element of
> the array, until the iteration is finished (x = 4).
> Then you try to call 4.each, which doesn't exist.
>
> See for comparison the 1.9 output with warnings enabled:
>
> iota ~ % ruby -vwe 'x = [1,2,3,4]; x.each{|x| p x }; x.each{|x| p x }'
> ruby 1.9.2p0 (2010-08-18 revision 29036) [x86_64-linux]
> -e:1: warning: shadowing outer local variable - x
> -e:1: warning: shadowing outer local variable - x
> 1
> 2
> 3
> 4
> 1
> 2
> 3
> 4
>
> As you can see, 1.9 shadows the outer variable, so the original is not changed.
>
> --
> Michael Fellinger
> CTO, The Rubyists, LLC

Ahh, that makes a lot of sense.  Thanks guys.

-Ryan