From: Mauricio Fernandez <mfp@...>
Date: 2006-07-10T23:13:46+09:00
Subject: Re: instance_exec

On Mon, Jul 10, 2006 at 08:29:46PM +0900, transfire@gmail.com wrote:
> > PS: I'm still curious about the reason for using a module.

* it allows instance_exec to work on frozen objects and immediate values
* it doesn't pollute Object with several methods (even if temporarily), only
  one module

> I think the idea was to save frm creting a singleton class, but at the
> expense of a module I don't see why either. Anyway, here the version I
> put in Facets. Please evaluate.
> 
> module Kernel
> 
>   # Like instace_eval but allows parameters to be passed.
>   #
>   # The implementation is thread-safe thanks to the
>   # Thread.current.object_id trick, but it doesn't work with
>   # immediate values (Fixnums and friends), and most
>   # importantly it bombs when given a frozen object.
>   def instance_exec(*args, &block)
>     mname =
> "__instance_exec(#{Thread.current.object_id},#{caller.object_id})"
>     Object.class_eval{ define_method(mname, &block) }
>     begin
>       ret = send(mname, *args)
>     ensure
>       Object.class_eval{ undef_method(mname) }
>     end
>     ret
>   end
> 
> end

heh you copied the comment from my blog entry[1] but that's not the
implementation it applied to ;). The above does work with immediate values and
frozen objects. But I now consider it flawed nonetheless, read

 http://eigenclass.org/hiki.rb?bounded+space+instance_exec

[1] http://eigenclass.org/hiki.rb?instance_exec
-- 
Mauricio Fernandez  -   http://eigenclass.org   -  singular Ruby