[ROOT] Persistency of TClass*

From: axel@fnal.gov
Date: Tue Jul 30 2002 - 15:48:30 MEST


Hi,

writing a TClass to file works without any problems, it's just that the 
read TClass is pretty much unusable. This makes kind of sense, as 
TClass is more or less a static object. But there are some cases where 
storing a TClass* would be helpful, e.g.: A map from TClass* to 
whatever-baseclass*, where the TClass* allows to identify and access 
objects deriving from whatever-baseclass.

Now, the suggestion I have is to make TClass store only the class name, 
and when reading back, to let TClass's streamer search for the TClass 
already instantiated which belongs to this class name. I believe this 
would be the naive expectation of what a persistent TClass* does.

The questions I have are:
* What do you (users and rootdev) think about that? Does it interfere 
with what other people do with a persistent TClass?
* Reading a member of type TClass*, is there any way ROOT can set this 
pointer to the TClass object already instatiated or will we end up with 
two instatiations for the same class?

Cheers, Axel.



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