From: 7stud -- <bbxx789_05ss@...>
Date: 2008-03-07T01:04:13+09:00
Subject: Re: Cloning a module and isolating it from the clone

7stud -- wrote:
> 
> However, I can't figure out a way to make a 'deep copy' where the object 
> that a reference refers to is also copied.  I tried deleting all the 
> class variables in the cloned module and then adding them back in with 
> new values--but they still refer to the same objects as the original 
> module, which is puzzling.
> 
> module A
>   @@num = 10
>   @@arr = [1, 2, 3]
> 
>   def A.get_num
>     @@num
>   end
> 
>   def A.set_num(x)
>     @@num = x
>   end
> end
> 
> puts A.get_num
> 
> new_meth = %q{
>   def B.remove(arr)
>     arr.each do |name|
>       remove_class_variable(name.to_sym)
>     end
>   end
> }
> 
> B = A.clone
> B.module_eval(new_meth)
> 
> class_vars = B.class_variables
> B.remove(class_vars)
> 
> puts "class variables in B:"
> p B.class_variables
> 
> class_vars.each do |name|
>   B.module_eval("#{name} = 0")
> end
> 
> B.set_num("hello")
> puts 'After cloning:'
> puts A.get_num
> puts B.get_num
> 
> A.set_num("goodbye")
> puts A.get_num
> puts B.get_num
> 
> --output:--
> 10
> class variables in B:
> []
> After cloning:
> hello
> hello
> goodbye
> goodbye
> 


I see now why that doesn't work.  Even though the code changes the class 
variables in B at the module scope, inside B's methods the class 
variables still refer to the same objects in A.  This demonstrates that:


test = %q{
  def B.get_my_num
    @@num   #this is the @@num in B at module scope that was erased and 
replaced
  end
}

A.set_num(35.2)
B.module_eval(test)
puts B.get_num   #retrieves the @@num inside get_num which is still a 
reference to objects in A
puts B.get_my_num

--output:--
35.2
0
-- 
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