RcppArmadillo pass user-defined function

(Sometime you need to use svn log ... on files to see how dated they are…)

I think a better use case is in my “port” of the C-based DEoptim to Rcpp / RcppArmadillo: RcppDE. In it, I allow the optimization routine to use either an R function (as DEoptim does) or a user-supplied compiled function — which is what you want here as I understand it.

There is a tiny bit of C++ scaffolding, but you should have no problem following that.

Edit on 2013-01-21 Below is a complete solution which I have also justed posted as this new post at the Rcpp Gallery — including some comments and sample usage.

// [[Rcpp::depends(RcppArmadillo)]]
#include <RcppArmadillo.h>

using namespace arma; 
using namespace Rcpp;

vec fun1_cpp(const vec& x) {    // a first function 
    vec y = x + x;
    return (y);
}

vec fun2_cpp(const vec& x) {    // and a second function
    vec y = 10*x;
    return (y);
}

typedef vec (*funcPtr)(const vec& x);

// [[Rcpp::export]]
XPtr<funcPtr> putFunPtrInXPtr(std::string fstr) {
    if (fstr == "fun1")
        return(XPtr<funcPtr>(new funcPtr(&fun1_cpp)));
    else if (fstr == "fun2")
        return(XPtr<funcPtr>(new funcPtr(&fun2_cpp)));
    else
        return XPtr<funcPtr>(R_NilValue); // runtime error as NULL no XPtr
}

// [[Rcpp::export]]
vec callViaString(const vec x, std::string funname) {
    XPtr<funcPtr> xpfun = putFunPtrInXPtr(funname);
    funcPtr fun = *xpfun;
    vec y = fun(x);
    return (y);
}

// [[Rcpp::export]]
vec callViaXPtr(const vec x, SEXP xpsexp) {
    XPtr<funcPtr> xpfun(xpsexp);
    funcPtr fun = *xpfun;
    vec y = fun(x);
    return (y);
}