From: Ill Everbe <illeverbe@...>
Date: 2010-06-05T02:26:50+09:00
Subject: class variables and modules

I am trying to keep a history of object state in a parent class using a
class variable. This works per example 1 using child method
update_state. but if i mixin a module to update_state (so as not to
repeat update_state every), per example 2 i get different behavior. i do
not understand why.
###########################   example 1  ########################
class A
 def initialize
  @@history=  []
  @@incoming_state = ['initial incoming state']
 end

 def  update_history
  @@history =  @@history.push( @@incoming_state.flatten)
 end

 def history
  @@history
 end
end

class B < A
 def new_state
  @another_state = ["new state"]
 end
 attr :another_state
 def update_state
  @@incoming_state = self.another_state
 end
end
a = A.new
b=B.new
b.new_state
b.update_state
b.update_history
b.update_state
b.update_history
p b.history
################################  example 2
################################

class A
 def initialize
  @@history=  []
  @@incoming_state = ['initial incoming state']
 end

 def update_history
  @@history = @@history.push( @@incoming_state.flatten)
 end

 def history
  @@history
 end
end

module Keeper
 def update_state
  @@incoming_state = self.another_state
 end
end

class B < A
 include Keeper
 def new_state
  @another_state = ["new state"]
 end
 attr :another_state
end

a = A.new
b=B.new
b.new_state
b.update_state
b.update_history
b.update_state
b.update_history
p b.history
-- 
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