From: Michael Fellinger <m.fellinger@...>
Date: 2010-09-25T11:55:13+09:00
Subject: Re: Using the same variable for an array and an iterator

On Sat, Sep 25, 2010 at 11:30 AM, Ryan <rdonahue@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