From: Jim Weirich <jweirich@...>
Date: 2002-03-17T11:03:31+09:00
Subject: Re: Could we subclass this way?

>>>>> "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)
----------------------------------------------------------------------

-- 
-- Jim Weirich     jweirich@one.net    http://w3.one.net/~jweirich
---------------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct, 
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)