[Rcpp-devel] Creating pointers to objects and wrapping them

[schattenpflanze at arcor.de]

> Now, for Rcpp classes to be aware of a custom wrap, you need some
> gymnatics, as described in the Rcpp-extending vignette.
> You need to include RcppCommon.h first, define you class and declare the
> custom wrap, then include Rcpp.h, then define you wrap.
> I'm pasting a full pass at it below.
Thanks a lot for your help!

> Things will get much simpler when we figure out a way to return classes
> exposed by modules and implement it.
I am looking forward to that :-).

Peter



> require( inline )
> require( Rcpp )
>
> settings <- getPlugin("Rcpp")
> settings$includes <- sprintf( "%s\n%s",
> '
> #include <RcppCommon.h>
> // B just stores an integer i here
> class B {
> public:
> B(int i) : i(i) {}
>
> int get_i() const {
> return i;
> }
>
> private:
> int i;
> } ;
> namespace Rcpp{
> template <>
> SEXP wrap( const B& object ) ;
> }
> ',
> settings$includes
> )
>
> inc <- '
> namespace Rcpp {
> template <>
> SEXP wrap( const B& object ){
> Language call( "new", Symbol( "B" ), object.get_i() ) ;
> return call.eval() ;
> }
> }
>
> // A contains a vector v of pointers to B
> class A {
> public:
> A(int n) : v(n) {}
>
> // THIS IS THE METHOD I WOULD LIKE TO IMPLEMENT:
> SEXP foo(int j) {
> if (!v[j]) {
> v[j] = new B(j);
> }
>
> // THIS DOES NOT WORK:
> return wrap(*v[j]);
> }
>
> private:
> std::vector<B*> v;
> } ;
>
> // Rcpp module exposing both A and B
> RCPP_MODULE(MyModule) {
> class_<A>( "A" )
> .constructor<int>(
> "Create an instance of A with a given number of pointers")
> .method("foo",
> &A::foo,
> "(Create and) get one of the objects of type B.")
> ;
>
> class_<B>( "B" )
> .constructor<int>("Create an instance of B from an int.")
> .property("i",
> &B::get_i)
> ;
> }
> '
>
> fx <- cxxfunction( , '
>
> ', includes = inc, settings = settings )
> populate( Module( "MyModule", getDynLib( fx ) ), env = .GlobalEnv )
>
> a <- new (A, 5)
> b <- a$foo(0)
> b$i