Best way to use c++ code from R package FOO in package BAR

Question

I am trying to define a function using Rcpp for speedup. The situation is as follows:

• I have a package FOO with a lot of C++ code (my own package and currently not

Answer 1

The RcppXts package does just that for a bunch of functions from the well-known xts package.

Edit: Here is some code from xts.

First, xts::src/init.c does the registration via a dozen or so declarations like

R_RegisterCCallable("xts","do_is_ordered",(DL_FUNC) &do_is_ordered);

Second, xts::inst/include/xtsApi.h provides a header for client packages with eg

SEXP attribute_hidden xtsIsOrdered(SEXP x, SEXP increasing, SEXP strictly) {
    static SEXP(*fun)(SEXP,SEXP,SEXP) = NULL;
    fun = (SEXP(*)(SEXP,SEXP,SEXP)) R_GetCCallable("xts","do_is_ordered");
    return fun(x, increasing, strictly);
}

Third, in a client package such as RcppXts we define this (using Rcpp Modules) as

function("xtsIsOrdered",
         &xtsIsOrdered,
         List::create(Named("x"),
                      Named("increasing") = true,
                      Named("strictly") = true),
         "Tests whether object is (strictly) (increasing) ordered");

which exposes it to R. We could equally well call the C function xtsIsOrdered from C++ code.

I removed the incorrect earlier comment that functions have to conform to 'SEXP in, SEXP out'.