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).
Leo
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