[Rcpp-devel] c++ class as argument in rcpp function (using modules)

Iirc, this is not implemented yet.

There is a chance we might add this feature in the future.

Cheers,

Romain



Le 21 d?c. 2011 ? 10:59, Yasir Suhail <yusuhail at gmail.com> a ?crit :

I need to pass a class as an argument in a function I am exposing to R.
From the skeleton package module, let us say that I have

class World {
public:
    World() : msg("hello"){}
    void set(std::string msg) { this->msg = msg; }
    std::string greet() { return msg; }
    void addMsg(World& w2) {
msg = msg + w2.msg;
    }
private:
    std::string msg;
};

However, this gives errors of the sort
/usr/local/lib/R/site-library/Rcpp/include/Rcpp/module/Module_generated_CppMethod.h:186:4:
error: invalid initialization of non-const reference of type ?World&? from
an rvalue of type ?World?
In file included from
/usr/local/lib/R/site-library/Rcpp/include/RcppCommon.h:306:0,
                 from /usr/local/lib/R/site-library/Rcpp/include/Rcpp.h:27,
                 from rcpp_module.cpp:1:
/usr/local/lib/R/site-library/Rcpp/include/Rcpp/traits/Exporter.h: In
constructor ?Rcpp::traits::Exporter<T>::Exporter(SEXPREC*) [with T = World,
SEXPREC* = SEXPREC*]?:
/usr/local/lib/R/site-library/Rcpp/include/Rcpp/as.h:51:51:   instantiated
from ?T Rcpp::internal::as(SEXPREC*, Rcpp::traits::r_type_generic_tag)
[with T = World, SEXPREC* = SEXPREC*]?
/usr/local/lib/R/site-library/Rcpp/include/Rcpp/as.h:75:89:   instantiated
from ?T Rcpp::as(SEXPREC*) [with T = World, SEXPREC* = SEXPREC*]?
/usr/local/lib/R/site-library/Rcpp/include/Rcpp/module/Module_generated_CppMethod.h:186:4:
  instantiated from ?SEXPREC* Rcpp::CppMethod1<Class, void,
U0>::operator()(Class*, SEXPREC**) [with Class = World, U0 = World&,
SEXPREC* = SEXPREC*]?
rcpp_module.cpp:86:1:   instantiated from here
/usr/local/lib/R/site-library/Rcpp/include/Rcpp/traits/Exporter.h:31:37:
error: no matching function for call to ?World::World(SEXPREC*&)?
rcpp_module.cpp:30:5: note: candidates are: World::World()
rcpp_module.cpp:28:13: note:                 World::World(const World&)
make: *** [rcpp_module.o] Error 1

Looking at http://dirk.eddelbuettel.com/code/rcpp/Rcpp-extending.pdf, it
seems that I can extend Rcpp::as to account for my classes, but I still
have two questions:
1. How do I define the constructor World(SEXP)? Is there a working example
somewhere for a user defined C++ class?
2. Can I also use pointers and pass-by-reference as these are more often
used in real C++ code.

In short, I'd appreciate a way to pass my C++ classes (as the class and
also by ref. or pointer) that have been exposed to R as arguments to
exposed functions. How do I achieve that?

Thanks!