From: Mark Hahn <mchahn@...>
Date: 2001-12-29T09:00:56+09:00
Subject: [ruby-talk:29603] promoting self to subclass (was extending method of class A ...)

Why not allow a method to "promote" it's object to a subclass of the object?
I've wanted to do this before in ruby and Java.  It should be somewhat easy
in ruby and nearly impossible in a static language.

How about making it:  self.promote(Klass)  or maybe Kernel::promote(Klass) ?
The same code that does the promotion could set the extra instance
variables.  Or, even better, the initializer of the subclass could be called
with params from the promote call: self = Klass.new(*params).  In general
this could be considered "assignment to self".

Where I've run into this need is when an initializer realizes that, based on
input params, there is a more specific class for this data.  Another case is
when an object is created and the "type" gets refined later.  If you want a
specific example of this being used, let me know.

----- Original Message -----
From: "Tomasz Wegrzanowski" <taw@users.sourceforge.net>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Friday, December 28, 2001 3:12 PM
Subject: [ruby-talk:29598] Re: extending method of class A to support
arguments of class B by promoting `self' to class B


> On Sat, Dec 29, 2001 at 07:59:42AM +0900, Mark Hahn wrote:
> >
> > > it should be promoted to Complex
> >
> > Is this possible?  I've wanted to change an object's type before inside
a
> > method of that object, but I didn't think it was possible.
> >
> > Or did you mean "return" a Complex object.  That is all you really need
to
> > do in the case you describe.
>
> I meant: temporary object of type Complex, initiated by Real object,
should be created,
> and method `*' of this temporary Complex object should be used instead of
method `*' of Real object.
>