[Rcpp-devel] R.e. loadRcppModules

Douglas Bates bates at stat.wisc.edu
Thu Apr 14 14:49:33 CEST 2011

On Thu, Apr 14, 2011 at 12:43 AM, Christian Gunning <xian at unm.edu> wrote:
> On Tue, Apr 12, 2011 at 11:07 PM, Romain Francois
> <romain at r-enthusiasts.com> wrote:
>>> Just to clarify --  does your plan include storing user-modified
>>> fields and properties in objects?  E.g. below, modtest with the msg
>>> set?
>> yes. Although the way I see it, this will require more work for the
>> developper, who would have to provide a serialization/deserialization couple
>> for his/her classes.
>> This is a nice goal for a future version.
> Am I naive to think that a 1-to-1 mapping between C++ object fields &
> properties and an S4 object might make sense?  This reduces the module
> developer's problem of serial/deserialization to 1) writing a
> constructor (and perhaps with validator) that takes an S4 object, and
> 2) writing a finalizer that populates a specified S4 object in the
> user's environment, tears down the C++ object (as per R Exts manual),
> and let's save() do the rest?
> It seems that, in theory, there's a canonical mapping between the
> names/types of fields/properties exposed in the RCPP_MODULE call and
> the proposed S4 object.  The main gotcha I see here is that any
> variable within a C++ object *not* exposed as a field/property must be
> viewed as a const to ensure consistency of the C++ object between
> write and re-construct...
> If this is off-base, feel free to ignore or point out good reading material :)

I don't think it is off-base.  I was planning something very similar
to that except that not every field/property would be saved.  I have
classes in which many of the properties are calculated on the fly and
I don't need to save those.  I just need to save enough information to
create the object again.

This approach would run into trouble if there were data fields in the
C++ object that could not be expressed as R objects.  However, it
seems to me that if the C++ object can be generated from R objects in
the first place you should be able to serialize enough information to
reconstruct it.

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