For now I managed the problem by checking a classname field in the xml, and then sending a SmallInteger with Number readFrom:'42'.
I would be quite interested in looking at your code. Where can I find this Magma you're talking about (if it is open source)?

Michel
>  You will not want to try generalizing your serialization/materialization quite so much.  There are "immediate" types and globals that you will not want to create new instances of.  Other examples are true, false and nil, Smalltalk, Processor, Transcript and others.
>  
>  I've been through a ton of this kind of stuff in having written Magma.  You might find looking at my serialization/materialization code helpful in this respect.
>  
>  Regards,
>    Chris
> 
> 
> 
> 
> 
> ------------------------------
>