From: hubert@... (Hubert Hung-Hsien Chang)
Date: 2002-03-17T22:39:02+09:00
Subject: Re: Could we subclass this way?

Thank you. Ron and Jim.

I don't know much about doing an abstract class in Ruby. 
Jim's method works ( by naming the 'variable' as method) and it does
the tricks.
Just curious how 'bad' my understanding on observable. What is wrong
with the following code? It is one of the 'failed' version of my
trying...


-----------------------
require 'observer'

class Monster
  include Observable

  attr_reader :tricks
  def initialize
    @tricks = []
    self.add_observer(self)
  end

  def spook(value)
      print "spooking:"
      notify_observers(value)
  end
end

class Ghost < Monster
  def update(value)
      print "Ghost scares", value,"\n"
  end
end

class Vampire < Monster
  def vampire_tricks
    @tricks
  end

   def update(value)
       print "Vampire scares", value,"\n"
   end

end

vamp = Vampire.new
vamp.spook("charles")

ghost = Ghost.new
ghost.spook("brown")


-----------------------







Jim Weirich <jweirich@one.net> wrote in message news:<m2heng6jdr.fsf@skaro.access.one.net>...
> >>>>> "Hubert" == Hubert Hung-Hsien Chang <hubert@cs.nyu.edu> writes:
> 
>     Hubert> Here is a question:
>     Hubert> Suppose I have a class called "Monster" with a instance variable 
>     Hubert> (@tricks) and two subclasses
>     Hubert> called  "Little_vampire" "Little_ghost" but I would like to name
>     Hubert> each of the subclass's @tricks differently. 
> 
>     Hubert> I would like to have @vampire_tricks, @ghost_tricks respectively.
>     Hubert> But I wuld still like to use the Monster's methods. And both
>     Hubert> @vampire_tricks and @ghost_tricks will refect the value
>     Hubert> of @tricks from "Monster"
> 
>     Hubert> I haven't successfully done it easily. Any way out?
> 
> Don't use "@" sytle names, Use accessor functions instead.  See the
> code below for an example.  Just remember, if you assign to an
> accessor, include "self."  ... otherwise Ruby will think its a local
> variable (see add_tricks for an example).
> 
> ----------------------------------------------------------------------
> class Monster
>   attr_reader :tricks
>   def initialize
>     @tricks = []
>   end
>   def show_tricks
>     puts "My Trickes are: #{tricks.join(' ')}"
>   end
> end
> 
> class Vampire < Monster
>   def vampire_tricks
>     @tricks
>   end
>   def vampire_tricks=(value)
>     @tricks = value
>   end
> 
>   def add_tricks(tricks)
>     self.vampire_tricks += tricks
>   end
> end
> 
> vamp = Vampire.new
> vamp.add_tricks %w(bite fly)
> ----------------------------------------------------------------------