[Rcpp-devel] inline plug-in linking

[Dirk Eddelbuettel]

On 16 November 2012 at 08:50, JJ Allaire wrote:
|     Anyhow, I think I am probably missing some linking info from my
|     inlinePlugIn statement.
| 
| 
| This is the key -- plugins that do linking are much more complicated than ones
| that rely on headers only. You can look at the Rcpp and RcppGSL packages as
| examples 

+1  ---  at this point I can only offer RcppGSL as (working!!) example. I
have a blog post planned to illustrate Rcpp attribute with it.  We have no
other example using a library.

| -- in short there needs to be a function inside the package that can
| cough up the correct library locations. If you get this far then your stuff

Exactly. Romain coughed up a very clever (as usual) but not-obvious-follow
(no comment ;-) scheme where the plugins essentially act as callback.  For
RcppGSL we have the added "fun" of needed to know where libgsl.* and
libgslcblas.* live -- which I solve with a detection at package load (when we
call the external gsl-config script) and storing the data in a package-global
little environment.

That works.  On windows, as always, you need more magic and I rely on the
sort-of plugic knowledge of where CRAN keeps its support libraries so that
packages can build against it.

If you supply your library with the package, then the callbacks are
self-contained within the package.  A bit of work but a) doable and b) a good
chance of being reliable.

| will work with inline and Rcpp::cppFunction, however people developing packages
| that want to link against your stuff will need custom Makevars entries (which
| you can configure the inline plugin to produce, but by now things have gotten
| pretty complicated for your users).
| 
| If you can manage to do header-only "linking" that will be much, much simpler.
| At the lowest level the key to this is R_GetCCallable. In Rcpp land there is a
| GetCppCallable equivalent that works with modules. You can see the use of this
| in the header file which is generated by Rcpp::interfaces(r, cpp).
| 
| If you want to expose the data structure using this mechanism then you could
| write a function like this:
| 
| // [[Rcpp::export]]
| Rcpp::List getModelStatistics() {
|    return StatController::getModelStatistics();
| }
| 
| And then compileAttributes will automatically generate the shim that calls
| GetCppCallable.

That is a fresh alternative.  And all this is work in progress, and your
feedback in testing and pushing it would also be appreciated.

So in short you can make it work, but you have to put in some work before it
all falls into place.  

Dirk

-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com