From: Massimiliano Mirra <list@...>
Date: 2001-12-30T02:11:22+09:00
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