From: Tomasz Wegrzanowski <tomasz.wegrzanowski@...>
Date: 2006-08-10T03:31:24+09:00
Subject: Re: How to make objects that can set $1 when obj =~ /(.)/ is called ?

On 8/8/06, Mauricio Fernandez <mfp@acm.org> wrote:
> On Tue, Aug 08, 2006 at 02:51:37PM +0900, Tomasz Wegrzanowski wrote:
> > class Foo
> >  def initialize(t)
> >    @text = t
> >  end
> >  def =~(x)
> >    @text =~ x
> >  end
> > end
> >
> > And it works for non-capturing regexps,
> > but when we want to capture something
> > $1 etc. are bound only within the =~ method,
> > and when the method returns they are
> > restored to their previous values.
> >
> > Foo.new("Hello") =~ /(e)/ # => 1
> > $1 # => nil
> >
> > Is it possible to somehow get =~ like that work,
> > even if it takes heavy metaprogramming hackery ?
>
> [ruby-talk:202600]

I finally got a working solution, using Binding.of_caller.
Not very elegant, but it works:

class Foo
    def =~(pattern)
        rv = (@text =~ pattern)
        Binding.of_caller {|binding|
            set_rx_vars = eval("lambda{|md| $~ = md}", binding)
            set_rx_vars.call($~)
            rv
        }
    end
end

-- 
Tomasz Wegrzanowski [ http://t-a-w.blogspot.com/ ]