[Rcpp-devel] Invoking class methods via XPtr<> objects in R

[Suresh Easwar]

All I want to do is obtain a shared-pointer equivalent in R to a C++ object and be able to do two things with it - 1. Invoke methods of the object via the shared-pointer and 2. pass the shared-pointer to the methods of other C++ class objects.

In Python, I am able to do this like so (Boost shared-ptrs are easily passed back and forth across the Python-C++ boundary using Boost-Python):
>>> aptr = mytest.get_aptr() # obtain a shared-pointer to an instance of class A
>>> aptr.f() # invoke method f() of class A via the pointer
>>> b = mytest.B(aptr) # construct object of class B invoking constructor that accepts a shared-pointer to object of class A.

I am looking for the equivalent in R (or at least a close enough idiom).

Thanks
suresh



________________________________
 From: Dirk Eddelbuettel <edd at debian.org>
To: Suresh Easwar <seaswar at yahoo.com> 
Cc: "rcpp-devel at lists.r-forge.r-project.org" <rcpp-devel at lists.r-forge.r-project.org> 
Sent: Wednesday, March 13, 2013 5:56 PM
Subject: Re: [Rcpp-devel] Invoking class methods via XPtr<> objects in R
 

On 13 March 2013 at 10:15, Suresh Easwar wrote:
| How does one invoke class methods via XPtr<T> objects in R? I get this error: Error in aptr$f : object of type 'externalptr' is not subsettable:

I don't understand what you are trying to do below, and do not have time to
understand and debug it for you.

Your example is also complicated as you mix XPtr and Modules.  Maybe you will
have more success walking in smaller steps --- and a working example of XPtr
via Rcpp is in the RcppDE package where I use XPtr to pass external
(user-given) C interface functions around to the optimiser.

Dirk

|  
| cpp file:
| #include <Rcpp.h>
| struct A {
| void f() {}
| };
| typedef Rcpp::XPtr<A> APtr;
| APtr getAPtr()
| {
| return APtr(new A);
| }
| struct B {
| B(APtr) { }
| };
| RCPP_MODULE(mytest)
| {
|                 Rcpp::function("get_aptr", &getAPtr);
|                 Rcpp::class_<A>("A")
|                                 .constructor()
|                                 .method("f", &A::f)
|                 ;
|                 Rcpp::class_<B>("B")
|                                 .constructor<APtr>()
|                 ;
| }
|  
| R session:
| R version 2.15.3 (2013-03-01) -- "Security Blanket"
| Copyright (C) 2013 The R Foundation for Statistical Computing
| ISBN 3-900051-07-0
| Platform: x86_64-unknown-linux-gnu (64-bit)
| > library(mytest)
| Loading required package: Rcpp
| > a <- new(A)
| > aptr <- get_aptr()
| > b <- new(B, aptr)
| > a$f()
| > aptr$f()       <- not sure how to invoke f() via aptr
| Error in aptr$f : object of type 'externalptr' is not subsettable
| > 
|  
| Thanks
|  
| Suresh
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-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com  
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