abc

abc.cpp

#include <Rcpp.h>
using namespace Rcpp ;

class abc {
public:
    abc( SEXP x ) : data(x){} 
    
    inline operator SEXP() const { 
        return data ;
    }    
       
    template <typename T>
    class Proxy {
    public:
        Proxy( abc& ref_, int index_ ) : ref(ref_), index(index_){}
        
        inline operator T() const { 
            return as<T>(ref.data[index]) ; 
        } 
        inline Proxy& operator=( const T& other ){
            ref.data = Rf_shallow_duplicate(ref.data);
            ref.data[index] = other ; 
            return *this ;
        }
        
    private:
        abc& ref ;
        int index ;
    } ;
    
    inline Proxy<NumericVector> a(){ return Proxy<NumericVector>(*this, 0); }
    inline Proxy<IntegerVector> b(){ return Proxy<IntegerVector>(*this, 1); }
    
        
private:
    List data ;
} ;

// [[Rcpp::export]]
abc test( abc obj ){
    obj.a() = NumericVector::create(1,2,3) ;
    obj.b() = seq(1, 5) ;
    return obj ;
}

/*** R
    obj <- structure( list( 1, 1L), class = "abc" )
    x <- test( obj )
    x
    obj
*/

output.txt

$ RcppScript /tmp/abc.cpp

> obj <- structure(list(1, 1), class = "abc")

> x <- test(obj)

> x
[[1]]
[1] 1 2 3

[[2]]
[1] 1 2 3 4 5

attr(,"class")
[1] "abc"

> obj
[[1]]
[1] 1

[[2]]
[1] 1

attr(,"class")
[1] "abc"