From: Jamis Buck <jgb3@...>
Date: 2004-01-06T04:59:06+09:00
Subject: Re: Basic Syntax for Extending Instances

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 end
>
>  def self.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
>
>date = Date.civil("DAY_OF_MONTH",2004,2,5)
>
>#Doh!
>puts date.date_precision # >> nil
>
>What is the proper syntax to make the date_precision attribute visible to
>the caller? I'm still trying to wrap my head around the notion of open
>classes and extending object instances...
>		
>Matt
>
>  
>

Well, it looks like the problem is that @date_precision is an "instance 
variable" of the object that represents the Date class, not of each 
instance of the Date class.  What you should do is capture the result of 
old_civil (which would be an instance of the class) and then set the 
date_precision attribute on it, like this:

  d = old_civil( *args )
  d.date_precision = args.shift
  return d

See if that helps any.

-- 
Jamis Buck
jgb3@email.byu.edu

ruby -h | ruby -e 'a=[];readlines.join.scan(/-(.)\[e|Kk(\S*)|le.l(..)e|#!(\S*)/) {|r| a << r.compact.first };puts "\n>#{a.join(%q/ /)}<\n\n"'