[Rd] [External] SET_COMPLEX_ELT and SET_RAW_ELT missing from Rinternals.h

[Konrad Siek]

I think all of my questions are answered. Thank you for your attention and
assistance.

The first question is whether you need to do this. Or, more to the
> point, whether it is safe to do this. In R objects should behave as if
> they are not mutable. Mutation in C code may be OK if the objects are
> not reachable from any R variables, but that almost always means they
> are private to your code so yo can use what you know about internal
> structure.
>
>
Thank you for the warning. I believe it's a legitimate use. In extremely
rough summary: A C function is called via .Call. Inside it, I create the
vector and use SET_*_ELT to populate it. I then return the vector. There is
some amount of complexity between creation and population, and the vector
can potentially be ALTREP.

I don't use SET_*_ELT on any vector I have not created.

COMPLEX0 is not in the API; it will probably be removed from the
> installed header files as we clean these up.
>

My mistake, thank you.

ALTCOMPLEX_SET_ELT is an internal implementation feature and not in the API.
> Again, it will probably be removed from the installed headers.
>
>
Thanks for the warning. I'll make sure to avoid it.

k

On Sat, Jul 3, 2021 at 2:37 AM <luke-tierney using uiowa.edu> wrote:

> On Thu, 1 Jul 2021, Konrad Siek wrote:
>
> > Thanks!
> >
> > So what would be the prescribed way of assigning elements to a CPLXSXP
> if I
> > needed to?
>
> The first question is whether you need to do this. Or, more to the
> point, whether it is safe to do this. In R objects should behave as if
> they are not mutable. Mutation in C code may be OK if the objects are
> not reachable from any R variables, but that almost always means they
> are private to your code so yo can use what you know about internal
> structure.
>

> If it is legitimate to mutate you can use SET_COMPLEX_ELT. I've added
> the declaration to Rinternals in R-devel and R-patched.
>
> For SET_COMPLEX_ELT(x, in v) is equivalent to COMPLEX(sexp)[index] = value,
> but that could change in the future it Set methods are supported.
>
> This does materialize a potentially compact object, but again the most
> important question is whether mutation is legitimate at all.
>
> > One way I see is to do what most of the code inside the interpreter does
> and
> > grab the vector's data pointer:
> >
> >     COMPLEX(sexp)[index] = value;
> >     COMPLEX0(sexp)[index] = value;
> >
>
> COMPLEX0 is not in the API; it will probably be removed from the
> installed header files as we clean these up.
>

> > This will materialize an ALTREP CPLXSXP though, so maybe the best way
> would
> > be to mirror what SET_COMPLEX_ELT does in Rinlinedfuns.h?
> >
> >     if (ALTREP(sexp)) ALTCOMPLEX_SET_ELT(sexp, index, value); else
> > COMPLEX0(sexp)[index] = vector;
>
> ALTCOMPLEX_SET_ELT is an internal implementation feature and not in the
> API.
> Again, it will probably be removed from the installed headers.
>
> Best,
>
> luke
>
> > This seems better, but it's not used in the interpreter anywhere as far
> as I
> > can tell, presumably because of the setter interface not being complete,
> as
> > you point out. But should I be avoiding this second approach for some
> > reaosn?
> >
> > k
> >
> > On Tue, Jun 29, 2021 at 4:06 AM <luke-tierney using uiowa.edu> wrote:
> >       The setter interface for atomic types is not yer implemented. It
> >       may
> >       be some day.
> >
> >       Best,
> >
> >       luke
> >
> >       On Fri, 25 Jun 2021, Konrad Siek wrote:
> >
> >       > Hello,
> >       >
> >       > I am working on a package that works with various types of R
> >       vectors,
> >       > implemented in C. My code has a lot of SET_*_ELT operations in
> >       it for
> >       > various types of vectors, including for CPLXSXPs and RAWSXPs.
> >       >
> >       > I noticed SET_COMPLEX_ELT and SET_RAW_ELT are defined in
> >       Rinlinedfuns.h but
> >       > not declared in Rinternals.h, so they cannot be used in
> >       packages. I was
> >       > going to re-implement them or extern them in my package,
> >       however,
> >       > interestingly, ALTCOMPLEX_SET_ELT and ALTRAW_SET_ELT  are both
> >       declared in
> >       > Rinternals.h, making me think SET_COMPLEX_ELT and SET_RAW_ELT
> >       could be
> >       > purposefully obscured. Otherwise it may just be an oversight
> >       and I should
> >       > bring it to someone's attention anyway.
> >       >
> >       > I have three questions that I hope R-devel could help me with.
> >       >
> >       > 1. Is this an oversight, or are SET_COMPLEX_ELT and
> >       SET_RAW_ELT not exposed
> >       > on purpose? 2. If they are not exposed on purpose, I was
> >       wondering why.
> >       > 3. More importantly, what would be good ways to set elements
> >       of these
> >       > vectors while playing nice with ALTREP and avoiding whatever
> >       pitfalls
> >       > caused these functions to be obscured in the first place?
> >       >
> >       > Best regards,
> >       > Konrad,
> >       >
> >       >       [[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
> >
> >
> >
>
> --
> 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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