[Rcpp-devel] Question about custom as and wrap functions

Dirk Eddelbuettel edd at debian.org
Thu Apr 25 12:28:18 CEST 2013


On 25 April 2013 at 10:47, Finlay Scott wrote:
| Thanks for the reply. I followed your suggestion and changed the name of the
| header file in /inst/include to 'asWrapExample.h' (the name of the package). I
| then changed the #include in the 'DummyClass_example.cpp' file to reflect that
| change. I also added:
| 
| PKG_CXXFLAGS=-I../inst/include
| 
| To the top of the Makevars file. However, I still get the same error. I have
| the feeling I'm missing something obvious. Thanks for the help so far.

Seems you are "just" having issues with package mechanics. 

You could try to look at an existing package as eg out RcppGSL which has had
this working for several years.  Try comparing all the relevant files
mentioned in the corresponding vignette Rcpp-extending.

Dirk
 
| Yours
| 
| Finlay
| 
| 
| 
| On Wed, Apr 24, 2013 at 5:41 PM, JJ Allaire <jj.allaire at gmail.com> wrote:
| 
|     Hi Finlay,
| 
|     If you name your include file the same name as your package then it will be
|     included automatically in RcppExports.cpp. The convention at work here is
|     that any custom as/wrap handlers should be accumulated (or referenced from)
|     that single file. This mirrors the existing convention used by Rcpp,
|     RcppArmadillo, RcppEigen, etc. to have a single global header file for
|     their C++ API.
| 
|     J.J.
| 
| 
|     On Wed, Apr 24, 2013 at 8:22 AM, Finlay Scott <drfinlayscott at gmail.com>
|     wrote:
| 
|         Hi
|         First of all I want to say how impressed I am with Rcpp. I think it is
|         going to be very useful for some of the packages I am developing. Thank
|         you very much for developing it.
| 
|         I have a question regarding writing custom as and wrap functions for my
|         own classes. Following the example in:
| 
|         http://gallery.rcpp.org/articles/custom-as-and-wrap-example/
| 
|         I can get my own minimal example to work with a very simple class, and
|         using the sourceCpp() function.
| 
|         The cpp code saved as a *.cpp file:
| 
|             #include <RcppCommon.h>
| 
|             class DummyClass {
|                 public:
|                     double value;
|             };
| 
|             namespace Rcpp {
|                 // non-intrusive extension via template specialisation
|                 template <> DummyClass as(SEXP dt);
|                 // non-intrusive extension via template specialisation
|                 template <> SEXP wrap(const DummyClass &d);
|             }
| 
|             #include <Rcpp.h>
| 
|             // define template specialisations for as and wrap
|             namespace Rcpp {
|                 template <> DummyClass as(SEXP dtsexp) {
|                 S4 dc_s4 = Rcpp::as<S4>(dtsexp);
|                 DummyClass dc;
|                 dc.value = dc_s4.slot("value");
|                 return dc;
|                 }
| 
|                 template <> SEXP wrap(const DummyClass &d) {
|                 Rcpp::S4 dc_s4("DummyClass");
|                 dc_s4.slot("value") = d.value;
|                 return Rcpp::wrap(dc_s4);
|                 }
|             }
| 
|             // [[Rcpp::export]]
|             DummyClass test_as_wrap(DummyClass dc, double multiplier){
|                 DummyClass dc_out;
|                 dc_out.value = dc.value * multiplier;
|                 return dc_out;
|             }
| 
| 
|         And the following R code compiles and calls the function:
| 
|             library(Rcpp)
|             sourceCpp("DummyClass_example.cpp")
|             setClass("DummyClass", representation(value = "numeric"))
|             dc <- new("DummyClass")
|             dc at value <- 23
|             test_as_wrap(dc, 4)
| 
|         This works just fine (like magic!) and the test_as_wrap() function is
|         happily called from R and returns an object of type DummyClass. I want
|         to use a similar approach in a package, so I made a minimal package
|         using:
| 
|         Rcpp.package.skeleton("asWrapExample",attributes=TRUE)
| 
|         I then split my original cpp file above into header and source code
|         files. In the /inst/include directory I placed a file
|         'DummyClass_example.h' which has:
| 
|             #include <RcppCommon.h>
| 
|             class DummyClass {
|                 public:
|                     double value;
|             };
| 
|             namespace Rcpp {
|                 // non-intrusive extension via template specialisation
|                 template <> DummyClass as(SEXP dt);
|                 // non-intrusive extension via template specialisation
|                 template <> SEXP wrap(const DummyClass &d);
|             }
| 
|         In the /src directory I placed a file 'DummyClass_example.cpp' which
|         has:
| 
|             #include "../inst/include/DummyClass_example.h"
|             #include <Rcpp.h>
| 
|             // define template specialisations for as and wrap
|             namespace Rcpp {
|                 template <> DummyClass as(SEXP dtsexp) {
|                 S4 dc_s4 = Rcpp::as<S4>(dtsexp);
|                 DummyClass dc;
|                 dc.value = dc_s4.slot("value");
|                 return dc;
|                 }
| 
|                 template <> SEXP wrap(const DummyClass &d) {
|                 Rcpp::S4 dc_s4("DummyClass");
|                 dc_s4.slot("value") = d.value;
|                 return Rcpp::wrap(dc_s4);
|                 }
|             }
| 
|             // [[Rcpp::export]]
|             DummyClass test_as_wrap(DummyClass dc, double multiplier){
|                 DummyClass dc_out;
|                 dc_out.value = dc.value * multiplier;
|                 return dc_out;
|             }
| 
|         When I try to compile the package I get this error message:
| 
|             RcppExports.cpp:9:1: error: 'DummyClass' does not name a type
| 
|         This is probably caused by the RcppExports.cpp not having an #include
|         for my DummyClass_example.h.
|         I understand the RcppExports.cpp file is automatically generated by the
|         magic of Rcpp so there is no point in adding it there by hand.
|         I've looked at the documentation but it is not clear to me how I can
|         tell RcppExports to also include my header file (if this is the source
|         of the problem).
|         Have I missed something in the documentation, or is there an example I
|         can follow?
|         Any help is appreciated.
| 
|         Yours
| 
|         Finlay
| 
| 
| 
| 
|        
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| 
| 
| 
| 
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-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com


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