R devel - May 2011 - serialization of external pointers

Hello,

I'm looking for examples of how to handle serialization of external 
pointers.

We use external pointers intensively in Rcpp for modules and one popular 
request is to have persistence. And I guess we need to be able to 
serialize/deserialize external pointers for this.

Also, module objects are all instances of reference classes, so maybe 
that can be handled at the R level ?

Romain

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Romain Francois
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On May 26, 2011, at 10:40 AM, Romain Francois wrote:
> Hello,
> 
> I'm looking for examples of how to handle serialization of external
pointers.
> 
> We use external pointers intensively in Rcpp for modules and one popular
request is to have persistence. And I guess we need to be able to
serialize/deserialize external pointers for this.
> 
> Also, module objects are all instances of reference classes, so maybe that
can be handled at the R level ?
> 
Reference classes have nothing to do with EXTPTR - they are simply built around
environments and as such have no issues with serialization.

As for EXTPTR, well, you can perform custom serialization (see refhook in
serialize() and unserialize()), so to answer your question, yes it's easy to
serialize EXPPTRs - you just have to provide functions that convert them to some
string representation and back.

So far, so good, but if you were thinking of using save()/save.image()/load() to
automatically serialize references in a workspace then the bad new is you
can't since there is no way to provide the hooks (that's why rJava
caches serialized representation inside the object so that you can restore the
pointers on load when you see a NULL pointer with a serialized cache - less
ideal solution, but doable).

Cheers,
Simon