[Rcpp-devel] correct way of making custom as and wrap functions available to other packages

[Thell Fowler]

Simon,

Not sure if it'll help but take a look at
https://github.com/Thell/RcppMultiPrecision/tree/wip-mpreal-wrappers

Particularly the flags.R, inline.R and mpreal_wrap_example.cpp. When I
built this Dirk pointed me to several
example packages in the thread [Rcpp-devel] Rcpp RMpfr mpreal to mpfr wrapping.

http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2012-April/003719.html

On Fri, Jul 17, 2015 at 10:12 AM, Simon Barthelmé
<simon.barthelme at gipsa-lab.fr> wrote:
> Hi Kevin
>
> Thanks for your answer. I've tried declaring them as inline but the compiler
> (clang, haven't tried gcc) issues a warning saying it's going to ignore the
> inline statement. I'm assuming this is because the declaration is actually a
> template specialisation but I haven't found a definitive answer.
> If I separate the declaration from the definition, the linker now complains
> as and wrap are missing. Using the interface:: attribute doesn't seem to
> help either.
>
> Best
>
> Simon
>
>
> Le 17/07/2015 16:56, Kevin Thornton a écrit :
>
> A good guess is that the as/wrap definitions in wrappers.h are the culprit
> (https://github.com/dahtah/imager/blob/master/inst/include/wrappers.h).  Try
> declaring them as inline, or separating the definition from the declaration.
>
> —Kevin
>
> On Jul 17, 2015, at 7:32 AM, Simon Barthelmé <simon.barthelme at gipsa-lab.fr>
> 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?
>
> Thanks!
>
> Simon Barthelme
>
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-- 
Sincerely,
Thell