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Documentation for .factory #937

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rstub opened this Issue Feb 7, 2019 · 1 comment

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rstub commented Feb 7, 2019

As far as I can tell the .factory method for Rcpp Modules is not documented yet. Recently I wrote the following example for a SO answer:

#include <Rcpp.h>
using namespace Rcpp;

// abstract class
class Base {
  public:
    virtual ~Base() {}
    virtual std::string name() const = 0;
};

// derived class
class Derived1: public Base {
  public:
    Derived1() : Base() {}
    virtual std::string name() const { return "Derived1"; }
};

// derived class
class Derived2: public Base {
  public:
    Derived2() : Base() {}
    virtual std::string name() const { return "Derived2"; }
};

Base *newBase( const std::string &name ) {
  if ( name == "d1" ){
    return new Derived1 ;
  } else if ( name == "d2" ){
    return new Derived2 ;
  } else {
    return 0 ;
  }
}

RCPP_MODULE(mod) {
  Rcpp::class_< Base >("Base")
    .factory<const std::string&>(newBase)
    .method("name", &Base::name)
  ;
}


/*** R
(dv1 <- new(Base, "d1"))
dv1$name()
(dv2 <- new(Base, "d2"))
dv2$name()
*/

Would you be interested in a PR that adds something along these lines to the Rcpp modules vignette?

@eddelbuettel

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eddelbuettel commented Feb 7, 2019

That sounds like a useful addition.

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