[Rcpp-devel] Re-using C++ code from a package with modules and defining linker flags using Rscript

Dirk Eddelbuettel edd at debian.org
Mon May 16 15:26:50 CEST 2011

Hi Jelmer,

On 16 May 2011 at 14:00, Jelmer Ypma wrote:
| Hi Dirk,
| thanks for your reply.
| > PS Also try
| >
| >   -e "QuadFunc:::CxxFlags()")
| >
| >   instead of
| >
| >   -e "library(QuadFunc); QuadFunc:::CxxFlags()")
| >
| >   as the ::: finds unexported symbols, that usually works from unloaded
| >   packages too.
| It works for unloaded packages that don't use modules. Since QuadFunc
| uses modules, this results in an error
| > Rscript -e "QuadFunc:::CxxFlags()"
| Error: .onLoad failed in loadNamespace() for 'QuadFunc', details:
|   call: value[[3L]](cond)
|   error: failed to load module QuadraticFunctionModule from package QuadFunc
| Execution halted
| whereas loading the library first doesn't
| > Rscript -e "library(QuadFunc); QuadFunc:::CxxFlags()"
| Loading required package: methods
| Loading required package: Rcpp
| -IC:/R/win-library/2.12/QuadFunc/include

I see, and I stand corrected. Using modules may have that requirement as a
| Perhaps I'm mis-using modules and should change something in my
| NAMESPACE or in R/zzz.R to get rid of this error? You can get the same
| error using Rcpp.package.skeleton( 'testmodA', module=TRUE ) (see the
| first email).
| > And because of LinkingTo: QuadFunc you may not need the CxxFlags.
| This is correct in this case. If another package links to QuadFuncVec,
| then I think the dependencies become a bit more complicated (but I
| might be mistaken here). Either the new package needs to add QuadFunc
| to the LinkingTo: field, or QuadFuncVec:::CxxFlags() should return the
| flags of all its dependencies. In this case I would choose to
| implement QuadFuncVec:::CxxFlags() returning its own flags and those
| from QuadFunc:::CxxFlags(). That way the user has to worry a bit less
| about dependencies. At least, that was what I came up with after some
| experimentation yesterday.

It should does not hurt. But for the compile step, you should only need the
header files, and R itself can point to those via LinkingTo.

Having a CxxFlags() function allows you to set other flags (maybe
-Dsomething) if you need it.  Nothing wrong with that -- I was merely trying
to point that you could make your life a little simpler.
| Are the LinkingTo: fields obtained for the current package only, or
| also the LinkingTo: fields of the packages it links to also included?
| E.g. packB has LinkingTo: packA, packC has LinkingTo: packB. Are the
| include paths of packA automatically added to packC? That would make
| the CxxFlags() unnecessary in this case.

I don't believe the DESCRIPTION files of dependent packages are read. So I
would just do this in DESCRIPTION for packC:

    LinkingTo: packA, packB

Does that help?


| Thanks,
| Jelmer

Gauss once played himself in a zero-sum game and won $50.
                      -- #11 at http://www.gaussfacts.com

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