From: Brian Candler <b.candler@...>
Date: 2009-03-02T06:02:51+09:00
Subject: Re: Marshal.load does not create new instances?

Ian Trudel wrote:
>> Ian, I'm not sure I understand what you want. AFAIK Marshal only works
>> if you have the same class definitions on both sides. Why is this a
>> problem for you?
> 
> This is actually how I use Marshal. It works fine if I have only one 
> version in one given Ruby program. The problem resides in loading 
> different files which may contain one version or another of the given 
> class definition. There are sometimes additional (or less) instance 
> variables

Instance variables are not part of the class definition at all - even 
when you're only talking about a single version of the class. Instance 
variables are dynamically set within each object instance. For example:

class Foo
  def bar
    @xyz = 123
  end
end

f = Foo.new    # no instance variables set at all

g = Foo.new
g.instance_variable_set(:@baz, 999)   # only @baz is set

Given this: it makes sense that serializing or deserializing an instance 
of Foo only takes into account what instance variables are set in that 
particular object, making no reference to the class definition.
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