From: luisealvarezb <luisealvarezb@...>
Date: 2009-09-19T11:15:09+09:00
Subject: Re: How to derive from DateTime?

On Sep 18, 7:19 pm, Ehsanul Hoque <ehsanul...@hotmail.com> wrote:
> > It looks to me that this is a case where you might be better served by using
> > composition and delegation rather than inheritance: instead of an Event
> > being a specialized DateTime, it would have a DateTime instance as an
> > instance variable and delegate certain methods (e.g., year, etc.) to that
> > instance variable.
>
> I agree with Christopher here. What you want is a proxy class. Here's a way you might implement it:
>
> class Event
>
>   def self.new( *args )
>
>     class << datetime = DateTime.new(*args)
>
>       def sweet
>
>         "what a sweet method"
>
>       end
>
>     end
>
>     datetime
>
>   end
>
> end
>
> You could also try this way:
>
> class Event
>     instance_methods.each { |m| undef_method m unless m =~ /(^__|^send$|^object_id$)/ }
>
> def initialize(*args)
>
>   @date_time = DateTime.new(*args)
>
> end
>
>         def method_missing(name, *args, &block)
>           @date_time.send(name, *args, &block)
>         end
> end
>
> I'm sure you can figure out what's happening here, and how to merge it with your own code.
>
> - Ehsan
>
> _________________________________________________________________
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Thank you for that code it looks like a good solution and will use
it.  However, I am left wondering why this anomaly with the
constructors in DateTime, does that not violate OO practices. How can
you not be able to inherit from a Class X and redefine it.

Thanks a lot...