Rails 3/3.2 mashalling

gistfile1.rb

class Foo
  def initialize(a)
    @a = a
  end
end
 
d = Marshal.dump(Foo.new(1))
=> "\x04\bIC:\bFoo{\x00\x06:\a@ai\x06"
 
Marshal.load("\x04\bIC:\bFoo{\x00\x06:\a@ai\x06")
# => works
 
# restart the console
class Foo < Hash
  def initialize(a)
    @a = a
  end
end
 
Marshal.load("\x04\bIC:\bFoo{\x00\x06:\a@ai\x06")
# => blows up with error