From: Sam Roberts <sroberts@...>
Date: 2005-02-10T23:21:22+09:00
Subject: Re: Subclassing Immutable objects (Time)

How about not sub-classing, and have Time be an implmentation detail
of your class? You can use method_missing to forward all methods
you don't specifically implement to your @time attribute, and you
can be mutable by just replacing your @time.

Sam

Quoteing tone_hole@yahoo.ca, on Thu, Feb 10, 2005 at 10:29:45PM +0900:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Hi folks,
> 
> I've been trying for a while to subclass Time, but i'm hitting some
> problems.  I tried simply overriding the methods in Time itself but
> after about 5 minutes i realized that i needed the old behaviour as
> well, so subclassing seems better.  I'm hitting the same problems with
> wrapping the object as well.
> 
> I know this question has been asked before but as far as i can tell they
> all seemed to deal with mutable objects (one notable example dealt with
> Array which has a nice replace() method available to it)
> 
> Because Time is immutable, there are a ton of methods that return new
> Time objects (class method parse, instance methods +, and - are the
> notable ones since i'm interested in these).  So if i write:
> 
> class MyTime < Time
> end
> 
> And do the following:
> 
> time = MyTime.parse("00:00:00") # returns Time
> time = MyTime.now + 50.0        # returns Time
> 
> Now, i could reimplement these methods in MyTime to return MyTime
> objects but I'm lost on how to do the conversion without something like
> Array's replace() method.  If i had it then i could do:
> 
> class MyTime < Time
> 
> ~  def MyTime.parse(str)
> ~    now.replace(Time::parse(str))
> ~  end
> 
> ~  def +(other)
> ~    replace(Time::+(other))
> ~  end
> 
> end
> 
> or something along those lines.
> 
> Anyone have any tips?
> 
> Thanks,
> Derek
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.2.4 (MingW32)
> 
> iD8DBQFCC2G5xPPkePIbSlwRAurHAJ90WXo/+bMwOD/AxQD7Nz3sUqvx9ACglIO5
> EcR7mKvC2Zb4x3amefaWnl4=
> =sYWa
> -----END PGP SIGNATURE-----
>