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Message: [QUOTE="Ill Everbe, post: 4664856"] 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 [/QUOTE]