From: Knut Franke <knut.franke@...>
Date: 2010-09-14T15:46:12+09:00
Subject: Re: Declarative relations between object attributes

Joel VanderWerf wrote:
> I wrote a library called observable for use in GUI MVC programming (with
> FXRuby), something along those lines. One nice feature was pattern
> matching on the changed value, so you could have separate handlers for
> different ranges etc. Ruby's #=== methods are very cool and somewhat
> underused. That might be a nice feature to add to your #observe method.
> 
> Here's the code:
> 
> http://redshift.sourceforge.net/observable/

Thanks for the link; I managed to miss that one when trying to google 
existing solutions. :-) I've taken the liberty to include some of the 
ideas in my code.

>      when_temperature 0..100 do
>        self.status = :on
>      end
> 
>      when_temperature 100..100000 do
>        self.status = :off
>      end

It appears that for this particular example, your API is nicer than 
mine. ;-) Here's another one (distilled from model-view.rb) which 
probably better illustrates the idea behind the cells approach:

class Model
   cell :name, :email, :role, :caption
   def initialize
      self.name = "Your Name"
      self.email = "user@example.com"
      self.role = "To"
      calculate(:caption) { "#{self.role}: #{self.name} <#{self.email}>" 
}
   end
end
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