From: Charles Oliver Nutter <charles.nutter@...>
Date: 2008-06-04T23:13:32+09:00
Subject: Re: instance_eval, regexp with block : losing $1

Vincent L. wrote:
> class Foo < Base
>   match :g, /(.)g$/i do
>     puts "$1 in passed block : #{$1}"  #Unfortunately $1 is lost !
>     'ggg'                              #so only hardcoded values :-(
>   end
> end
...
> But I don't manage to get these to work...
> I need to get $1, $2, etc. special values
> in the block I pass in Base subclasses.
> How can I do that ?

The backref and numbered group globals are tied to the containing 
method/class body. So here, where you have a match call with a block 
inside a class body, the capture would be the one that lives in that 
body. That's part of the problem with relying on these special variables 
and the side effect of e.g. gsub: you can't implement the same behavior 
in Ruby because certain core methods like gsub have "special" side 
effects impossible to emulate.

- Charlie