From: "Lipper, Matthew" <mlipper@...>
Date: 2004-01-06T05:12:26+09:00
Subject: Re: Basic Syntax for Extending Instances

Thank you! 

I'll have to do a little re-reading to understand this fully; so, your
version adds an "instance instance variable" (as opposed to a "class
instance" variable)?

Thank again!

Matt




-----Original Message-----
From: Austin Ziegler [mailto:austin@halostatue.ca]
Sent: Monday, January 05, 2004 2:54 PM
To: ruby-talk@ruby-lang.org
Subject: Re: Basic Syntax for Extending Instances


On Tue, 6 Jan 2004 04:42:26 +0900, Lipper, Matthew wrote:
> Hey everybody,
> Given the following extension to the Date class:
> class Date
>   attr_accessor :date_precision
>   class << self
>     alias_method :old_civil, :civil
>     def civil(*args)
>       # How to make this visible?
>       @date_precision = args.shift
>       puts "#{@date_precision}" if($VERBOSE) # >> DAY_OF_MONTH
>       return old_civil(*args)
>     end
>   end
> end
> 
> date = Date.civil("DAY_OF_MONTH",2004,2,5)

> #Doh!
> puts date.date_precision # >> nil

Try:

  class Date
    attr_accessor :date_precision
    class << self
      alias_method :old_civil, :civil
      def civil(*args)
        precision = args.shift
        _civil = old_civil(*args)
        _civil.date_precision = precision
        _civil
      end
    end
  end

  date = Date.civil("DAY_OF_MONTH", 2004, 2, 5)
  puts date.date_precision

In your original code, you were adding @date_precision to the
singleton class Date (a "class instance" variable).

-austin
--
austin ziegler  * austin@halostatue.ca * Toronto, ON, Canada
software designer * pragmatic programmer * 2004.01.05
                    * 14.48.27