Le 1 sept. 2014 à 11:48, Dr Gregory Jefferis <jeffe...@mrc-lmb.cam.ac.uk> a
écrit :
> Hello,
>
> I have a more or less complete Rcpp(Eigen) dependent package that exposes a
> pair of C++ classes to R using RcppModules;the C++ classes (which implement k
> nearest neighbour search trees) differ only in their scalar storage type
> (float vs double) and are called WKNND and WKNNF. For future
> flexibility/maintenance I would have like to convert the C++ classes to
> templated code. Is it possible to use RcppModules to expose template classes?
> I know that Rcpp in general can be used with template classes, but the
> RcppModules manual does not seem to mention this.
>
> I have tried to implement this by simple translation of my existing code to a
> single WKNN class and then defining types for WKNND and WKNNF (i.e. double
> and float). However this falls over with errors/notes indicating that the
> automatic wrap/conversion of Eigen types is failing to pick up the typedef.
> Error:
>
> In file included from WKNND.cpp:1:
> In file included from
> /Library/Frameworks/R.framework/Versions/3.1/Resources/library/Rcpp/include/Rcpp.h:27:
> In file included from
> /Library/Frameworks/R.framework/Versions/3.1/Resources/library/Rcpp/include/RcppCommon.h:169:
> In file included from
> /Library/Frameworks/R.framework/Versions/3.1/Resources/library/Rcpp/include/Rcpp/as.h:25:
> /Library/Frameworks/R.framework/Versions/3.1/Resources/library/Rcpp/include/Rcpp/internal/Exporter.h:31:28:
> error: no matching constructor for initialization of 'WKNN<double>'
> Exporter( SEXP x ) : t(x){}
> ^ ~
> and notes like:
>
> ./WKNN.h:14:8: note: candidate constructor (the implicit copy constructor)
> not viable: cannot convert argument of incomplete type 'SEXP' (aka 'SEXPREC
> *') to 'const WKNN<double>'
> struct WKNN {
> ^
> ./WKNN.h:16:3: note: candidate constructor not viable: cannot convert
> argument of incomplete type 'SEXP' (aka 'SEXPREC *') to 'const
> Eigen::Map<Eigen::Matrix<double, Dynamic, Dynamic> >'
> WKNN(const Eigen::Map<Eigen::Matrix<T, Dynamic, Dynamic> > data, bool
> buildtree=true);
> ^
>
> So is there a way round this? Do I have to write an explicit wrap function?
> Do I have to give up on using RcppModules altogether? Any advice or pointers
> to a package already doing this would be much appreciated. And of course big
> thanks to Dirk, Romain and Douglas et al for these great packages.
>
> Best wishes,
>
> Greg.
>
> PS Code on this branch:
>
> https://github.com/jefferis/nabor/tree/feature/template-WKNN
>
> with these 2 commits making the changes:
>
> https://github.com/jefferis/nabor/commit/fa85ddae5187f1e93801d7ec36d1d78923384cc6
> https://github.com/jefferis/nabor/commit/9ff93e63023b2f6d9c7ddad54fb7d1f503685b86
Hi,
This looks related to what RCPP_EXPOSED_CLASS does, perhaps because your class
comes from a template, you could try RCPP_EXPOSED_CLASS_NODECL instead. The
only difference is that it does not add the class forward declaration, so you'd
have to have it after you have defined or declared your class.
Romain
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