Hi<div><br></div><div>I looked up the previous thread <span style="background-color:rgb(255,255,255)">"</span><span style="background-color:rgb(255,255,255);font-family:Times">Creating pointers to objects and wrapping them"</span><font face="arial, helvetica, sans-serif"><span style="background-color:rgb(255,255,255)"> from </span><span style="background-color:rgb(255,255,255)"><a href="http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2011-April/002170.html">http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2011-April/002170.html</a>, and it seems that providing a specialization of the wrap<>() function can help us return classes. Perhaps similarly, one could provide a specialization of the as<>() function for arguments? While wrap is implemented with the Language("new" ... function, is there any example of an as<>() specialization for custom classes? The vignette (</span><a href="http://dirk.eddelbuettel.com/code/rcpp/Rcpp-extending.pdf">http://dirk.eddelbuettel.com/code/rcpp/Rcpp-extending.pdf</a></font><span style="background-color:rgb(255,255,255);font-family:arial,helvetica,sans-serif">) shows a declaration for as, but no definitions.</span></div>
<div><div><font face="arial, helvetica, sans-serif"><br></font></div><div><font face="arial, helvetica, sans-serif">Thanks!</font></div><div><font face="arial, helvetica, sans-serif"><br></font></div><div><font face="arial, helvetica, sans-serif">Yasir<br>
</font><div><font face="arial, helvetica, sans-serif"><span style="background-color:rgb(255,255,255)"><br></span></font></div><div><font face="arial, helvetica, sans-serif"><span style="background-color:rgb(255,255,255)"><br>
</span><br></font><div class="gmail_quote">On Wed, Dec 21, 2011 at 5:45 AM, <span dir="ltr"><<a href="mailto:romain@r-enthusiasts.com">romain@r-enthusiasts.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF"><div>Iirc, this is not implemented yet. </div><div><br></div><div>There is a chance we might add this feature in the future. </div><div><br></div><div>Cheers, </div><div><br></div><div>Romain<br><br>
<div><br></div></div><div><br>Le 21 déc. 2011 à 10:59, Yasir Suhail <<a href="mailto:yusuhail@gmail.com" target="_blank">yusuhail@gmail.com</a>> a écrit :<br><br></div><div><div class="h5"><div></div><blockquote type="cite">
<div>I need to pass a class as an argument in a function I am exposing to R. From the skeleton package module, let us say that I have<div><br></div><div><div>class World {</div><div>public:</div><div> World() : msg("hello"){}</div>
<div> void set(std::string msg) { this->msg = msg; }</div><div> std::string greet() { return msg; }</div><div> void addMsg(World& w2) {</div><div><span style="white-space:pre-wrap"> </span>msg = msg + w2.msg;</div>
<div> }</div><div>private:</div><div> std::string msg;</div><div>};</div><div><br></div></div><div>However, this gives errors of the sort</div><div><div>/usr/local/lib/R/site-library/Rcpp/include/Rcpp/module/Module_generated_CppMethod.h:186:4: error: invalid initialization of non-const reference of type ‘World&’ from an rvalue of type ‘World’</div>
<div>In file included from /usr/local/lib/R/site-library/Rcpp/include/RcppCommon.h:306:0,</div><div> from /usr/local/lib/R/site-library/Rcpp/include/Rcpp.h:27,</div><div> from rcpp_module.cpp:1:</div>
<div>/usr/local/lib/R/site-library/Rcpp/include/Rcpp/traits/Exporter.h: In constructor ‘Rcpp::traits::Exporter<T>::Exporter(SEXPREC*) [with T = World, SEXPREC* = SEXPREC*]’:</div><div>/usr/local/lib/R/site-library/Rcpp/include/Rcpp/as.h:51:51: instantiated from ‘T Rcpp::internal::as(SEXPREC*, Rcpp::traits::r_type_generic_tag) [with T = World, SEXPREC* = SEXPREC*]’</div>
<div>/usr/local/lib/R/site-library/Rcpp/include/Rcpp/as.h:75:89: instantiated from ‘T Rcpp::as(SEXPREC*) [with T = World, SEXPREC* = SEXPREC*]’</div><div>/usr/local/lib/R/site-library/Rcpp/include/Rcpp/module/Module_generated_CppMethod.h:186:4: instantiated from ‘SEXPREC* Rcpp::CppMethod1<Class, void, U0>::operator()(Class*, SEXPREC**) [with Class = World, U0 = World&, SEXPREC* = SEXPREC*]’</div>
<div>rcpp_module.cpp:86:1: instantiated from here</div><div>/usr/local/lib/R/site-library/Rcpp/include/Rcpp/traits/Exporter.h:31:37: error: no matching function for call to ‘World::World(SEXPREC*&)’</div><div>rcpp_module.cpp:30:5: note: candidates are: World::World()</div>
<div>rcpp_module.cpp:28:13: note: World::World(const World&)</div><div>make: *** [rcpp_module.o] Error 1</div></div><div><br></div><div>Looking at <a href="http://dirk.eddelbuettel.com/code/rcpp/Rcpp-extending.pdf" target="_blank">http://dirk.eddelbuettel.com/code/rcpp/Rcpp-extending.pdf</a>, it seems that I can extend Rcpp::as to account for my classes, but I still have two questions:</div>
<div>1. How do I define the constructor World(SEXP)? Is there a working example somewhere for a user defined C++ class?</div><div>2. Can I also use pointers and pass-by-reference as these are more often used in real C++ code.</div>
<div><br></div><div>In short, I'd appreciate a way to pass my C++ classes (as the class and also by ref. or pointer) that have been exposed to R as arguments to exposed functions. How do I achieve that?</div><div><br>
</div><div>Thanks!</div>
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