From: Austin Ziegler <halostatue@...>
Date: 2004-06-29T02:19:35+09:00
Subject: Re: Is it considered Harmful?

On Tue, 29 Jun 2004 01:48:26 +0900, Sean O'Dell <sean@celsoft.com> wrote:
> On Monday 28 June 2004 09:27, Austin Ziegler wrote:
> > On Tue, 29 Jun 2004 00:58:22 +0900, Sean O'Dell <sean@celsoft.com> wrote:
> > > #class= can only be called on existing objects, so it can't prevent
> > > initialization from happening (it already happened before you can even
> > > make the call). The takeover class inherits an already-initialized
> > > object.  I'm not sure how else to say that. The object is already
> > > initialized, #class= cannot prevent that. Both classes, the old and the
> > > new, work with an already-initialized object.
> >
> > So ... with your modifications, I can safely do:
> >
> >   foo = Object.new
> >   foo.class = Tempfile
> >   foo.write "bar"
> 
> Safely, yes.  Usefully, no.  Tempfile can't do much with just an Object
> instance, and since its methods expect its own data and nothing else, it
> really would just complain that it can't do anything useful.

No, it wouldn't work safely, and your protestations to the contrary
won't change that -- Tempfile *expects* that by time you would call
#write on an object of its class, the tempfile will be open. You have
introduced a situation, with #class=, where not only is the tempfile
not open, it simply does not exist.

You also demonstrate a fundamental misunderstanding of the difference
between #class= and #become; they are not related.

  foo = Object.new
  foo.class = Tempfile

is not the same as:

  foo = Object.new
  foot = Tempfile.new("foot")
  foo.become(foot)

All references to foo now become references to foot, and foo itself is
released for garbage collection. It should really be quite obvious why
one is safer than the other.

-austin
-- 
Austin Ziegler * halostatue@gmail.com
               * Alternate: austin@halostatue.ca