This seems fairly un-C++-like, and rather prone to breakage. What if the iteration order is changed (accidentally or not) during some update in the future? Clients relying on a specific order will break.
All that said if you wish to support this all you have to do is implement your own iterator and provide begin/end methods (or free functions with those names) to provide access. Then the iterator takes care of remembering which attribute it's currently looking at and provides it when dereferenced.
