RcppParallel using References in workers

Question

I have been experiment with using references for speed improvements. The (not working) trivial example below, probably won't see any improvements. However, I think by not copying the data into a separate (cost) function, should save some time for a non trivial example.

As for now I have the example in an R-project as three c++ files:

header

#ifndef ExampleInternal_H
#define ExampleInternal_H

namespace ExampleInternal{

#include <RcppArmadillo.h>
#include <RcppParallel.h>
#include <Rcpp.h>

void myfuncA(arma::rowvec &vec_in, arma::colvec& data){

  vec_in.at(1) = vec_in.at(0)*arma::accu(data);

}

struct PARALLEL_WORKER : RcppParallel::Worker{

  arma::mat &input_output;
  const arma::colvec &data_in;

  PARALLEL_WORKER(arma::mat &input_output, const arma::colvec &data_in);
  void operator()(std::size_t begin, std::size_t end);
};

}

#endif

Function

#include <RcppArmadillo.h>
#include <RcppParallel.h>
#include "ExampleInternal.h"
using namespace ExampleInternal;

// [[Rcpp::export]]
arma::mat Parallelfunc(int Len_in, const arma::colvec data_in){

  arma::mat input(Len_in, 2, arma::fill::zeros);
  for(unsigned int i = 0; i < Len_in; i ++){
    input.at(i, 0) =i;
    }

  ExampleInternal::PARALLEL_WORKER worker(input, data_in);
  parallelFor(0, Len_in, worker);
  return input;
}

Parallel Worker

#include <RcppArmadillo.h>
#include <RcppParallel.h>
#include "ExampleInternal.h"

using namespace RcppParallel;
using namespace ExampleInternal;

namespace ExampleInternal{

PARALLEL_WORKER::PARALLEL_WORKER(arma::mat &input_output, const arma::colvec &data_in) : input_output(input_output), data_in(data_in) {}
  void PARALLEL_WORKER::operator()(std::size_t begin, std::size_t end){

    for(unsigned int k = begin; k < end; k ++){

      ExampleInternal::myfuncA(input_output.row(k), data_in);

    }

  }

}