Le 24/10/2019 à 18:23, Leonardo Silvestri a écrit :
On 24 October 2019 at 16:01, Serguei Sokol wrote:
| I'am trying to find a way to access class methods of one Rcpp
package | (say pkgM) from C++ code in another one (say pkgA).
| If it were simple C++ routines and not class methods, the way is
known | and even automatized. E.g. if I generate pkgM with
| | Rcpp::Rcpp.package.skeleton("pkgM", module=TRUE)
| Rcpp::compileAttributes("pkgM")
| | then in pkgM/src/RcppExports.cpp we can see
| | | static const R_CallMethodDef CallEntries[] = {
| {"_pkgM_rcpp_hello_world", (DL_FUNC) &_pkgM_rcpp_hello_world, 0},
| ...
| | As far as I understand, it registers _pkgM_rcpp_hello_world for
use with | R_GetCCallable from other packages. And it is a consequence
of preceding
| rcpp_hello_world() with "// [[Rcpp::export]]".
| If I add "// [[Rcpp::interfaces(r, cpp)]]" in
pkgM/src/rcpp_module.cpp | it produces
pkgM/inst/include/{pkgM.h,pkgM_RcppExports.h} and
| | static const R_CallMethodDef CallEntries[] = {
| ...
| {"_pkgM_RcppExport_registerCCallable", (DL_FUNC) |
&_pkgM_RcppExport_registerCCallable, 0},
| ...
| but still nothing for methods and functions from RCPP_MODULE.
| | So my question, what is a canonical way (if defined) to expose
class | methods (via RCPP_MODULE or any other mechanism) in such a way
that they | become callable from C++ code of another package? Am I
supposed to | register them manually in some way using |
_pkgM_RcppExport_registerCCallable()? And if so, how can I retrieve
them | in C++ code of another package?
From the top of my head I would say "No" for the simple reason that
all R
does (and this is the same for all other foreign-function interfaces)
has to
be C based. Hence no class methods. C++ signatures are compiler
dependent,
and have been avoided for that reason for as long as we had them.
So I fear you need plain C wrappers for every member function you want to
expose. I could of course be wrong -- if someone else has
counter-examples I
would be all ears!
Dirk
--
http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org
I believe Dirk is correct in saying the traditional mechanism won't work
for non-static member functions, but if the C++ code is fully contained
in header files in 'inst/include', then it's possible to access that
code from another package since there's no library that one needs to
link against. I believe that's the mechanism that Rcpp itself uses.
Things get ugly when one tries to link to another package's library.
I've tried a few experiments with Dirk's help
(https://github.com/lsilvest/linktest), but haven't found a reliable way
to make this portable (things break when packages are installed
pre-compiled).
Thanks for sharing, it saved me some iterations of trying.
I tested a direct exposing of member function with
R_RegisterCCallable("pkgM", "Num__setx", (DL_FUNC) &Num::setX);
and then passing a call with a first argument as pointer to an object.
It worked on my Linux with gcc 8.3 with a warning at
(DL_FUNC) &Num::setX. Then I read here
https://isocpp.org/wiki/faq/pointers-to-members that such kind of cast
are explicetly prohibeted as inducing undefined behavior. So my working
example was just a chance.
As Dirk suggested, wrapping a method in a plain C-line function worked.
Here, for the record, main steps:
0. put Num class definition in pkgM/inst/include/pkgM.h
1. in pkgM/Num.cpp
void wrap_Num__setx(Num *pobj, double val) {
pobj->setX(val);
}
2. in pkgM/RcppExports.cpp add
R_RegisterCCallable("pkgM", "Num__setx", (DL_FUNC) &wrap_Num__setx);
to R_init_pkgM(DllInfo *dll) { ...
3. in pkgA/DESCRIPTION
LinkingTo: Rcpp, pkgM
Depends: pkgM
4. in pkgA/rcpp_hello_world.cpp
// [[Rcpp::export]]
void a_setx(XPtr<Num> xp, double val)
{
XPtr<Num> p(xp);
static void (*fun)(Num*, double) = NULL;
if (fun == NULL) fun = (void (*)(Num*, double))
R_GetCCallable("pkgM","Num__setx");
fun(p, val);
}
5. in R session
library(pkgA) # loads pkgM too
num=Num$new() # created with pkgM infrastructure
a_setx(num@.xData$.pointer, 100)
num$x
#[1] 100
Best,
Serguei.
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