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From: Ill Everbe on 4 Jun 2010 13:26
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
--
Posted via http://www.ruby-forum.com/.

From: Robert Dober on 4 Jun 2010 16:22
On Fri, Jun 4, 2010 at 7:26 PM, Ill Everbe <illeverbe(a)yahoo.com> wrote:
Short answer: Do not use class variables, period! Because they are
shared amongst subclasses.
Long answer: Ok that's exactly what you want.... include Keeper into A
and leave the subclasses alone ;)
--
The best way to predict the future is to invent it.
--Alan Kay

From: Ill Everbe on 4 Jun 2010 17:09
Robert Dober wrote:
> On Fri, Jun 4, 2010 at 7:26 PM, Ill Everbe <illeverbe(a)yahoo.com> wrote:
> Short answer: Do not use class variables, period! Because they are
> shared amongst subclasses.
> Long answer: Ok that's exactly what you want.... include Keeper into A
> and leave the subclasses alone ;)

Much thanks from illeverbe
--
Posted via http://www.ruby-forum.com/.

From: Rein Henrichs on 5 Jun 2010 15:15
As a side note:

On 2010-06-04 10:26:50 -0700, Ill Everbe said:

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

Array#push modifies the receiver, so you can simply say:

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

or even:

@@history << @@incoming_state.flatten

--
Rein Henrichs
http://puppetlabs.com
http://reinh.com

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