to_xml

# note that last item is User class
a = [10, [20, 30, ["helo", "world"]], [1.2, 1.3], {:foo => :bar}, User]

puts a.to_xml

<?xml version="1.0" encoding="UTF-8"?>
<objects type="array">
  <object type="integer">10</object>
  <object type="array">
    <object type="integer">20</object>
    <object type="integer">30</object>
    <object type="array">
      <object>helo</object>
      <object>world</object>
    </object>
  </object>
  <object type="array">
    <object type="float">1.2</object>
    <object type="float">1.3</object>
  </object>
  <object>
    <foo>bar</foo>
  </object>
  <object>User</object>
</objects>