[R-pkg-devel] R package with external C++ library

[Ege Rubak]

Hi,

I would like to port Google's s2-library for spherical geometry (see 
e.g. https://github.com/micolous/s2-geometry-library for a fork on 
GitHub). It is not a standard library that can easily be installed on 
various systems, so I would like to include the source code in the R 
package. The catch is that I would like to modify the source code as 
little as possible :-)

I have package everything and added configure scripts and a tiny 
R-function that calls one of the C++-functions (using the antiquated .C 
interface for now -- that will of course be changed) in this repo:
https://github.com/spatstat/s2

It compiles into a working package on Ubuntu (travis-ci + my laptop), 
OSX (travis-ci), and Windows (appveyor + my surface pro), but R CMD 
check produces some warnings (and a note about the size of the shared 
object, but I assume that is less important).

The main things seem to be related to (travis log is at 
https://travis-ci.org/spatstat/s2/jobs/149578339):

1. Deprecated C++ headers <ext/hash_set> and <ext/hash_map>.

2. Compiled code that calls entry points which might terminate R or 
write to stdout/stderr.

Is it hopeless to get on CRAN with warnings like these?
I'm not very used to writing C/C++ code, but I guess 1. can be fixed by 
a few sed commands with the replacement headers and corresponding new 
function names. Point 2. can probably also be fixed with a reasonable 
effort, but I haven't investigated yet, and I would like an opinion from 
the list before spending more time on this. In more generality the 
question could be phrased something like:

"When including C++ code from an upstream library which you do not 
control should R CMD check be completely spotless or is some flexibility 
to be expected in these circumstances?"

Cheers,
Ege

PS: Extra question (prehaps particularly aimed at Dirk): When I will 
actually start to use the C++ library I expect it could be beneficial to 
use Rcpp. I have seen RcppModules mentioned somewhere, and I wonder if 
such an external C++ library would make sense to interface via 
RcppModules (again aiming at changing upstream sources as little as 
possible)?

-- 
Ege Rubak, Associate Professor,
Department of Mathematical Sciences, Aalborg University
Fredrik Bajers Vej 7G, 9220 Aalborg East, Denmark
Phone: (+45)99408861
Mobile: (+45)30230252
Email: rubak at math.aau.dk