[Rcpp-devel] Cost of RCPP_EXPOSED_CLASS pre/post population (post substantially lower)

[Thell Fowler]

Possibly interesting results; at least to anyone who may typically
construct and populate a class in the constructor...

> Rcpp::sourceCpp('VectorCreation.cpp')

> v1 <- function(len) {v<-make_preVector(len); v$vec }

> v2 <- function(len) {v<-make_postVector(); v$populate(len); v$vec }

> identical( v1(10), v2(10) )
[1] TRUE

> library(microbenchmark)

> microbenchmark( v1(6250000), v2(6250000), times=20 )
Unit: milliseconds
        expr       min        lq    median       uq      max neval
 v1(6250000) 11.556459 11.912062 17.983704 24.14962 45.93693    20
 v2(6250000)  9.158329  9.338543  9.516148 15.83003 40.87731    20


_File: VectorCreation.cpp <gist::  https://gist.github.com/Thell/9242382 >


// [[Rcpp::plugins("cpp11")]]

#include <RcppCommon.h>

class preVector;
RCPP_EXPOSED_CLASS(preVector)

class postVector;
RCPP_EXPOSED_CLASS(postVector)

#include <Rcpp.h>

using namespace Rcpp;

class preVector {
public:
  std::vector< int > vec;
  preVector(int len) : vec(len)
  {
    int i(0);
    while( i < len ) {
      vec[i] = i;
      i++;
    }
  }
};
preVector make_preVector( int len ) { return preVector(len); }
RCPP_MODULE(preVector){
  class_< preVector >("preVector")
    .constructor< int >()
    .field("vec", &preVector::vec)
  ;
  function( "make_preVector", &make_preVector );
}

class postVector {
public:
  std::vector< int > vec;
  postVector() {}
  void populate(int len) {
    vec = std::vector< int >(len);
    int i(0);
    while( i < len ) {
      vec[i] = i;
      i++;
    }
  }
};
postVector make_postVector() { return postVector(); }
RCPP_MODULE(postVector){
  class_< postVector >("postVector")
    .constructor()
    .method("populate", &postVector::populate )
    .field("vec", &postVector::vec)
  ;
  function( "make_postVector", &make_postVector );
}


/*** R
v1 <- function(len) {v<-make_preVector(len); v$vec }
v2 <- function(len) {v<-make_postVector(); v$populate(len); v$vec }
identical( v1(10), v2(10) )

library(microbenchmark)
microbenchmark( v1(6250000), v2(6250000), times=20 )
*/


-- 
Sincerely,
Thell
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