[Rd] [External] Questions regarding ALTREP_SET_ELT APIs

[Wang Jiefei]

Hi Luke,

Thanks for your quick response. I appreciate your help.

Best,
Jiefei

On Tue, Jul 30, 2019 at 12:41 PM Tierney, Luke <luke-tierney using uiowa.edu>
wrote:

> On Tue, 30 Jul 2019, Wang Jiefei wrote:
>
> > Hi all,
> >
> > I'm wondering if there is any way to define a `SET_ELT` function for an
> > ALTREP class? I see there are ` ALTINTEGER_SET_ELT` etc. functions
> exported
> > in Rinternal.h, but there is no corresponding ALTREP APIs to define them.
> > The only way to set the value of an ALTREP is through a pointer, which
> will
> > require that the ALTREP data is in memory. Is it on purpose?
>
> For now, yes. We do support a Set_elt method for ALTSTRING classes but
> not yet for others. I seem to recall that there are some issues with
> going there for others, but we'll probably take a closer look later
> this year.
>
> One thing to keep in mind is that the R pass-by-value semantics
> require that C code duplicate an object for which MAYBE_REFERENCED is
> true, and the assumption in existing code is that duplicate returns an
> object that can safely be mutated. That places a lot of limitations on
> what can be done. You can see some notes on the issues in the
> README.md and the vignette in
> https://github.com/ALTREP-examples/Rpkg-mutable.
>
> Best,
>
> luke
>
> > Will there be
> > any plan to develop these ALTREP set element APIs?
> >
> > Best,
> > Jiefei
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
>
> --
> Luke Tierney
> Ralph E. Wareham Professor of Mathematical Sciences
> University of Iowa                  Phone:             319-335-3386
> Department of Statistics and        Fax:               319-335-3017
>     Actuarial Science
> 241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
> Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu
>

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