From: Mark Hahn <mchahn@...>
Date: 2001-12-30T05:17:35+09:00
Subject: [ruby-talk:29649] Re: promoting self to subclass (was extending method of class A ...)

Your solution is what I have used.  But it is much longer than the one line
I proposed.

I think that this is a cool concept that other languages don't have and
should be considered for ruby.

----- Original Message -----
From: "Massimiliano Mirra" <list@chromatic-harp.com>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Saturday, December 29, 2001 9:11 AM
Subject: [ruby-talk:29636] Re: promoting self to subclass (was extending
method of class A ...)


> On Sat, Dec 29, 2001 at 09:00:56AM +0900, Mark Hahn wrote:
> > 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.
>
> Not sure I'm following you, but what about this:
>
> class Foo
>   def Foo.create(changing_param, *args)
>     case changing_param
>     when Integer
>       SuperFoo.new(*args)
>     when String
>       MegaFoo.new(*args)
>     else
>       Foo.new(*args)
>     end
>   end
>
>   def initialize(a, b, c)
>     p "Foo: #{a}, #{b}, #{c}"
>   end
> end
>
> class SuperFoo < Foo
>   def initialize(a, b, c)
>     p "SuperFoo: #{a}, #{b}, #{c}"
>   end
> end
>
> class MegaFoo < Foo
>   def initialize(a, b, c)
>     p "MegaFoo: #{a}, #{b}, #{c}"
>   end
> end
>
> Foo.create('string', 1, 2, 3)  # -> "MegaFoo: 1, 2, 3"
>
> Foo.create(999, 1, 2, 3)       # -> "SuperFoo: 1, 2, 3"
>
> Foo.create([9, 8, 7], 1, 2, 3) # -> "Foo: 1, 2, 3"
>
>
> It might cover your first case (initializer).
>
> Massimiliano
>