From: Ehsanul Hoque <ehsanul_g3@...>
Date: 2009-09-19T14:58:24+09:00
Subject: Re: How to derive from DateTime?

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>=20
> Thank you for that code it looks like a good solution and will use
> it.  However=2C I am left wondering why this anomaly with the
> constructors in DateTime=2C does that not violate OO practices. How can
> you not be able to inherit from a Class X and redefine it.
>=20
> Thanks a lot...
>=20

Actually=2C there's no anomaly really=2C as far as I know. There's some bug=
 in the code. I have no idea where=2C your code seems fine to me=2C and it =
could just be because of the way the DateTime class was implemented. But yo=
u can in fact redefined constructors=2C and it works fine. Try this for exa=
mple (just an adaptation of your code):

class Foo
  def initialize(x)
    @x =3D x
    @message =3D "message from foo"
  end
  attr_accessor :message=2C :x
end

class Bar < Foo
  class << self
    alias :old_new :new
    def new(x)
      obj =3D old_new
      obj.send :initialize
      obj
    end
  end
  =20
  def initialize
    @message =3D "message from bar"
  end
 =20
  attr_accessor :message
end



f =3D Foo.new(0)


f.message   #=3D> "message from foo"

f.x       #=3D> 0

b =3D Bar.new(0)

b.message       #=3D> "message from bar"
b.x         #=3D> nil   (I actually don't understand why this is=2C someone=
 else might be able to explain)

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