Nesting Rcpp functions

user_13427882 0
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Is it possible to nest Rcpp functions in each other? I have a dummy example right here:

cppFunction(
  'int add3(int x) {
  return x+3;
}')

cppFunction(
  'int add4(int x) {
  return add3(x)+1;
}')

add3(2)

This does not work. How can I make this work?

Edit: Okay, so I followed Dirk's advice and now I have a test.cpp file:

#include <Rcpp.h>

using namespace Rcpp;

// [[Rcpp::export]]
int add3(int x) {
    return x + 3;
}

// [[Rcpp::export]]
int add4(int x) {
    return add3(x)+1;
}

Which I load in R with sourceCpp("test.cpp"). Now I can use both functions in R and they work although one function calls the other function.

rcpp r
1 Answers

The answers to your question get a little technical quickly, but are all provided in the Rcpp Attributes vignette, and have been for a long time.

First off, you are more-or-less misusing cppFunction(). It is made for quick and simple one-off function tests. Not for writing "infrastructure" or more complex code. For which you should use sourceCpp(), or better still, use a package.

If you switch you code to sourceCpp() and the [[Rcpp::export]] tag you will notice (in verbose=TRUE mode, or in package building) that the exported functions get 'transliterated' into other functions that R calls.

So yes you can nest functions, as you can in C / C++. Nothing is taken from you. But you cannot call the inner, nested function from R but that is possible with the API offered to us by R and which we use (and free you from interfacing directly). It only has SEXP .Call(functionanme, SEXP a, SEXP b,...) as an interface. I.e. a different signature.

But on the C / C++ you can nest, provided you compile your code differently.

user_1433050
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