Ruby Class Redefinition

class_fu.rb

class Foo #v1
  def initialize(value)
    @value = value
  end
  
  def add
    37 + @value
  end
end

# create a Foo and serialize it
@foo_v1_instance = Foo.new(9)
@foo_instance_marshalled = Marshal.dump(@foo_v1_instance)

# redefine Foo, but save the old version in an instance var
@foo_v1 = Object.send(:remove_const, :Foo)
class Foo #v2
  def initialize
    @value = value
  end

  def mult
    37 * @value
  end
end

# create a Foo of the new version by unmarshalling the old version instance
@foo_v2_instance = Marshal.load(StringIO.new(@foo_instance_marshalled))

# undefine Foo
@foo_v2 = Object.send(:remove_const, :Foo)

# redefine Foo v1 without any source code
Object.send(:const_set, 'Foo', @foo_v1)

# resurrect our original Foo instance with the old Foo code base
@foo_v1_instance_reborn = Marshal.load(StringIO.new(@foo_instance_marshalled))