From: dblack@...
Date: 2003-01-18T08:14:23+09:00
Subject: Re: quick: it responds, it evaluates, and is not empty

Hi --

On Sat, 18 Jan 2003, ahoward wrote:

> that's at least the second time i've forgotten about that method.  i've never
> really understood why there cannot be
>
>   class Symbol
>     def initialize str
>       ...
>     end
>   end
>
> which i would NOT forget about...

See <http://www.rubygarden.com/article.php?sid=110> -- there was a
(rejected) RCR for Symbol.new, with some commentary from Matz.

> [I wrote:]
>
> > For me there are two problems with the exception-wrapping idiom:
> > speed, and the absence of an exception which precisely and uniquely
> > corresponds to "this object did not respond to that message."
> > NameError can represent a case where the method got called but,
> > itself, tried to call a non-existent method on an object.
>
> good point.  but wouldn't simply returning NACK from method missing accomplish
> this?  (see my other post)

Yes, I would assume it would be implemented as some kind of hook into,
and/or wrapper around, method_missing.  The issues this would raise
would then have to do with minimizing impact on objects that already
have a method_missing... so I think it would have to be included or
extended into particular objects (including classes) selectively.

(And it's probably not thread-safe, because no ideas I ever have are
thread-safe :-)

Here's my latest iteration, based on code posted in this thread and my
own tinkerings:

  class Method
    NACK = Class.new.class_eval {
      require 'singleton'
      include Singleton
    }.instance

    module Nacker
      def method_missing(*args)
	NACK
      end
    end
  end

  # Class-wide inclusion
  class A
    include Method::Nacker
  end

  # Object extension
  s = "abc"
  s.extend(Method::Nacker)

  # Demo
  p A.new.no_such_method == Method::NACK  # true
  p s.no_such_method == Method::NACK      # true


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav