From: Brian Candler <lists@...>
Date: 2012-09-13T16:57:04+09:00
Subject: Re: Marshaling classes

Unfortunately Marshal.dump doesn't dump even instance variables of a 
class, just the name of the class.

--8<----
class Dog
   @quantity = 5
   def self.change_quantity=(n)
     @quantity = n
   end
   def self.show_quantity
     @quantity
   end
end

Dog.change_quantity = 99

File.open('anyfile.mrs', 'w+') do |f|
  Marshal.dump(Dog, f)
end

Dog.change_quantity = 50

Dog2 = Marshal.load(File.open('anyfile.mrs'))

puts Dog.show_quantity   # 50
puts Dog2.show_quantity  # 50
puts Dog.object_id == Dog2.object_id   # true
--8<----

$ hexdump -C anyfile.mrs
00000000  04 08 63 08 44 6f 67                              |..c.Dog|
00000007

So I guess it's up to you to iterate over instance_variables:

--8<----
class IVDumper
  def initialize(klass)
    @klass = klass
    @ivs = {}
    klass.instance_variables.each do |k|
      @ivs[k] = klass.instance_variable_get(k)
    end
  end
  def restore
    @ivs.each do |k,v|
      @klass.instance_variable_set(k,v)
    end
    @klass
  end
end
def IVDumper(k)
  IVDumper.new(k)
end

Dog.change_quantity = 99

File.open('anyfile.mrs', 'w+') do |f|
  Marshal.dump(IVDumper(Dog), f)
end

Dog.change_quantity = 50

Marshal.load(File.open('anyfile.mrs')).restore

puts Dog.show_quantity   # 99
--8<----

You can probably make this more transparent, e.g using _dump/_load 
methods in IVDumper

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