From: Joe Van Dyk <joe.vandyk@...>
Date: 2004-11-12T04:13:30+09:00
Subject: Re: automatically call function on attribute set

Joel VanderWerf wrote:
> Joe Laughlin wrote:
>> I have a class that represents an airplane.  This class
>> has a bunch of data members: x/y/z positions, x/y/z
>> velocities, pitches, rolls, etc.  What I did is let the
>> user configure what different attributes the airplane
>> had in a YAML config file, then have the airplane class
>> read in that file and setup attr_accessors for each
>> attribute in the file.
>>
>> I have another object (call it airplane_drawing) that is
>> responsible for drawing this airplane on the screen.  It
>> needs to have access to some of the attributes of the
>> airplane, and it needs have some of its own attributes
>> changed whenever airplane's attributes changes.
>>
>> What is the best way to get airplane_drawing to be
>> notified whenever some attribute of airplane is changed?
>> Should I have a thread (or similar) that checks the
>> airplane object to see if anything's changed?
>>
>> I hope I've explained this well enough for people to
>> understand... I feel like this is a fairly common thing
>> to do, but I'm not sure of the best way to do it.
>
> Another approach is the observable lib on RAA
> (http://raa.ruby-lang.org/list.rhtml?name=observable).
>
>
>    require 'observable'
>
>    class Airplane
>      extend Observable
>
>      observable :x, :y, :z
>
>      def initialize(x = 0, y = 0, z = 0)
>        @x, @y, @z = x, y, z
>      end
>
>      def fly
>        self.x += 1   # don't use @x=, or else no
>      notification end
>    end
>

What is the difference between self.x and @x?

Thanks,
Joe