From: Bertram Scharpf <lists@...>
Date: 2005-01-31T16:58:21+09:00
Subject: Re: Restoring global variables?

Hi,

Am Montag, 31. Jan 2005, 08:10:47 +0900 schrieb Robert Klemme:
> 
> "Bertram Scharpf" <lists@bertram-scharpf.de> schrieb im Newsbeitrag 
> news:20050130214711.GA30470@homer.bertram-scharpf...
> >do I have any possibiliy to save and restore global
> >and instance variables? I think of something like:
> >
> > user@host$ cat l.rb
> > class C ; @@i = 0 ; end
> > $g = ""
> >
> > cache_globals { load 'm.rb' }
> > assert $g == "" and C.instance_eval { @@i.zero? }
> >
> > user@host$ cat m.rb
> > C.instance_eval { @@i += 99 }
> > $g << "foo"
> > user@host$
> >
> >There are several workarounds, for example starting another
> >process. What is the smartest way to do it?
> 
> This is one way that's better than another process.
> 
> module Kernel
> private
>  def cache_globals
>    store = {}
>    global_variables.each {|v| store[v] = eval(v)}
>    begin
>      return yield
>    ensure
>      store.each do |n,v|
>        begin
>          eval "#{n}=v"
>        rescue NameError, SyntaxError, ArgumentError
>          # ignore
>        end
>      end
>    end
>  end
> end
> 
> $f = 0
> p $f
> cg { $f = 100; p $f }
> p $f

Another nice workaround. Two caveats:

  * Newly created variables aren't destroyed.
  * side effects:

    irb(main):002:0> eq=eval '$='
    => false
    irb(main):003:0> eval '$= = eq'
    (eval):1: warning: modifying $= is deprecated
    => false

> You can also create something with #trace_var:
> http://www.ruby-doc.org/core/classes/Kernel.html#M001741

Instantiating about 50 trap routines? No. Besides that, the
above solution could be bypassed using a trace. It's a
security question I asked.

Thanks very much anyway, so far.

Bertram

-- 
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-scharpf.de