From: Mark Hubbart <discordantus@...>
Date: 2004-12-04T11:02:52+09:00
Subject: Re: any way to manipulate variables and bindings?

On Fri, 3 Dec 2004 21:42:47 +0900, Robert Klemme <bob.news@gmx.net> wrote:
> 
> "itsme213" <itsme213@hotmail.com> schrieb im Newsbeitrag
> news:I7Jrd.100267$jq5.22882@fe2.texas.rr.com...
> 
> 
> > def foo
> >     bar [:a, :b, :c]
> >     a
> >     b
> >     c
> > end
> >
> > I would like a, b, and c to be local variables with values 1, 2, 3
> > (positions of :a, :b, :c). Is there some implementation of
> >     def bar (symbol_list)
> >         symbol_list.each_with_index { |s, i|
> >             ???
> >         }
> >     end
> > that will do this?
> 
> As Mark pointed out, you can't get this to work because of the compile
> time decisions Ruby takes.

I should clarify: Ruby will set the variables, they are just
inaccessible unless you assign to them at some point in that binding's
context:

mark@eMac% ruby   
eval "a = 23"
p a
^D
-:2: undefined local variable or method `a' for main:Object (NameError)

mark@eMac% ruby          
eval "a = 23"
a += 19
p a
^D
42

So, as long as you assign to them anywhere in that context, it's okay.
even if it's after they have been set once. head.spin(:rapidly)

I think the reason for this is that there was a tradeoff made: to do
what you want to do would require that variables be checked at
runtime, not eval-time. This would prevent early detection of errors
related to variable names. I guess it was decided that the error
detection was more important than a slightly more flexible/dynamic
local variable setup.

cheers,
Mark