Before we go any further, I should disclaim that I know almost nothing about go, although to put this in perspective I did not know much about C++ before I started to work on Rcpp.

Before I started to cook this recipe, I needed to check some ingredients: - go can make shared libraries (.so) - R can link to those

Casual sunday browsing led me to tick the first box, with Building shared libraries in Go: Part 1 which is about calling go from python.

The second box is automatically checked through some experience.

package main

import "C"

//export DoubleIt
func DoubleIt(x int) int {
        return x*2 ;
}

func main() {}

The code above (in file doubler/main.go) defines the go function DoubleIt. By importing the "C" package and exporting the DoubleIt symbol we make sure that we we will build a shared library we can call from C.

go build -o libdoubler.so -buildmode=c-shared ./doubler

We also need some C code that will act as a proxy between this shared library and the C R api can understand. I’ll skip over the details, if you have not seen this, it means that Rcpp has done a good job over the years.

#include <R.h>
#include <Rinternals.h>

extern int DoubleIt() ;

SEXP godouble(SEXP x){
  return Rf_ScalarInteger( DoubleIt( INTEGER(x)[0] ) ) ;
}

So we define a SEXProof function godouble that calls DoubleIt. We can R CMD SHLIB it:

$ R CMD SHLIB -L. -ldoubler rgo.c
clang -I/Library/Frameworks/R.framework/Resources/include -DNDEBUG   -I/usr/local/include   -fPIC  -Wall -g -O2  -c rgo.c -o rgo.o
clang -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/Library/Frameworks/R.framework/Resources/lib -L/usr/local/lib -o rgo.so rgo.o -L. -ldoubler -F/Library/Frameworks/R.framework/.. -framework R -Wl,-framework -Wl,CoreFoundation

And then we can finally call it from R:

$ Rscript -e 'dyn.load("rgo.so"); .Call("godouble", 21L)'
[1] 42

This is the beginning of a beautiful friendship