Dear list,
As a follow-up to last week's discussion, the simplest solution is
indeed inlining.
You can define your wrapper functions in a header, myPackage.h,
containing inline function definitions rather than declarations:
----
namespace Rcpp {
template <> inline myClass as(SEXP foo){
//
}
template <> inline SEXP wrap(myClass &bar){
//
}
----
You put the header in inst/include, and add -I../inst/include to
PKG_CPPFLAGS.
Your wrapper functions are now available to other packages via a
Depends: statement in DESCRIPTION, and you can define a plugin as well
by adding a file to R/ containing:
inlineCxxPlugin <- Rcpp:::Rcpp.plugin.maker(
include.before = "#include <myPackage.h>",
package = "myPackage"
)
The mistake I was making was to write inline template <> instead of
template <> inline, which the compiler ignores (rather than issue a
syntax error). Thanks everybody for your input!
Best
Simon
Le 17/07/2015 20:23, Dirk Eddelbuettel a écrit :
On 17 July 2015 at 17:41, Simon Barthelmé wrote:
| Thanks Dirk! I'm not sure how to ensure that only one compilation unit
| includes the file (the package would have to get rid of RcppExports.cpp
| somehow, or stuff everything in there). I'm also not sure I understand
| what you mean by enforcing purity but I'll investigate. The third
Kevin hit that as well: inline function, and/or templates. You essentially
need to avoid having the symbol be created several times over as that gets
the linker error.
Dirk
| solution is the same one Kevin suggested, I think, and I haven't managed
| to get it to work.
|
| Best
|
| Simon
|
| Le 17/07/2015 17:09, Dirk Eddelbuettel a écrit :
| > On 17 July 2015 at 16:32, Simon Barthelmé wrote:
| > | Dear list,
| > |
| > | For a package I'm developing (https://github.com/dahtah/imager/) I had
| > | to write custom "as" and "wrap" functions for third-party classes. I'd
| > | like to make these wrappers accessible to other developers via inline
| > | C++ as well as LinkingTo directives (so that they can be used in other
| > | packages).
| > | So far I've only managed the former: I have a header file in
| > | inst/include, called "wrappers.h", that contains the full
| > | implementations of my custom as and wrap functions. I've written a
| > | custom inline plugin and everything works fine. However, LinkingTo
| > | doesn't work: wrappers.h gets included in multiple object files and I
| > | get linking errors (the linker complains about multiple declarations of
| > | "as" and "wrap").
| > | I understand RcppArmadillo manages to get around the problem but I can't
| > | figure out how. What's the correct way of doing this? Is there a way of
| > | making as and wrap inline functions so that it's safe to have
| > | header-only implementations?
| >
| > Am at work now with my wrapped in another issue but I think one way of
fixing
| > this is to ensure that only one compilation unit includes the file. Another
| > is to make sure the header file is "pure" in the 'just templates' sense so
| > that you do not get multiple instantiations. A third is to use #define
| > statements to separate declarations (used for other packages) from
definitions
| > and instantiations (which your package uses).
| >
| > I definitely had this design issue and managed to address it. With a bit
| > more coffee I may even remember which package that was in...
| >
| > Dirk
| >
|
_______________________________________________
Rcpp-devel mailing list
Rcpp-devel@lists.r-forge.r-project.org
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
