Odtnhj

Let's say I want to build a very simple package in R that wraps c++ code.

My test project would be called bananas.

Let's say I have a folder called "bananas", where inside I have two other folders one called c++ and one called R.

Inside the c++ folder I have folder called include that contains the bananas.hpp header file (with the class definition):

#ifndef BANANAS_H
#define BANANAS_H

class Bananas

 public:
 void add_banana();
 int get_bananas();

 protected:
 int number_of_bananas;
;

#endif

Outside include there is the bananas.cpp file that implements the methods of bananas.hpp:

#include "include/bananas.hpp"
using namespace std;

void Bananas::add_banana()
 // Return False if edge already existed
 number_of_bananas ++;


int Bananas::get_bananas()
 return number_of_bananas;

now in my R folder I have a the wrapper.cpp file that uses Rcpp library to export c++ classes inside R as a module:

#include <Rcpp.h>
#include "include/bananas.hpp"

using namespace Rcpp;

RCPP_EXPOSED_CLASS(Bananas)

RCPP_MODULE(Bananas_cpp)

 class_<Bananas>("BananasCPP")
 .default_constructor()
 .method("add_banana", &Bananas::add_banana)
 .method("get_bananas", &Bananas::get_bananas)
 ;

Note that right now #include "include/bananas.hpp" does not mean anything, but in the future this file will be added inside source.
Finally I have my main concern which a R wrapper of this class under:

require(R6)
library(Rcpp)

# For exposing the error
print(ls(all.names = TRUE))

# Load Module
bcpp <- Module("Bananas_cpp", PACKAGE="RBananasC", mustStart = TRUE)$BananasCPP

Bananas <- R6Class("Bananas", list(
 bn = new(bcpp),
 print_bananas = function() print(self$bn$get_bananas()),
 banana_tree = function(d) 
 for(row in 1:d)
 self$bn$add_banana()
 
 
 ))

Now when running the setup.R file in my main directory which looks as follows:

require(Rcpp)

# Make a base package
unlink("RBananasC", recursive=TRUE)
Rcpp.package.skeleton(name = "RBananasC", list = character(), 
 path = ".", force = FALSE, 
 cpp_files = c("bananas/R/wrapper.cpp", "bananas/c++/bananas.cpp", "bananas/c++/include/bananas.hpp"))
dir.create("RBananasC/src/include")
file.rename("RBananasC/src/bananas.hpp", "RBananasC/src/include/bananas.hpp")
install.packages("RBananasC", repos=NULL, type="source")

# See that Bananas_cpp works
library(RBananasC) #Without this line it doesn't work

print(Module("Bananas_cpp", PACKAGE="RBananasC", mustStart = TRUE)$BananasCPP)
bcpp <- Module("Bananas_cpp", PACKAGE="RBananasC", mustStart = TRUE)$BananasCPP
ban <- new(bcpp)
ban$add_banana()
print(ban$get_bananas())

# Make the desired package
unlink("RBananas", recursive=TRUE)
Rcpp.package.skeleton(name = "RBananas", list = character(), 
 path = ".", force = FALSE, 
 code_files = c("bananas/R/bananas.R"), cpp_files = c("bananas/R/wrapper.cpp", "bananas/c++/bananas.cpp", "bananas/c++/include/bananas.hpp"))
dir.create("RBananas/src/include")
file.rename("RBananas/src/bananas.hpp", "RBananas/src/include/bananas.hpp")
install.packages("RBananas", repos=NULL, type="source")

I have a very strange behaviour inside my bananas.R file, that has to do with the fact that Bananas_cpp module of my package is not visible and so I cannot access the class BananasCPP upon installation.
On the other hand if I ignore the file bananas.R I can import the BananasCPP from the module Bananas_cpp of the package RBananasC, I created using Rcpp.package.skeleton.

To sum up the total file structure looks like:

.
├── bananas
│   ├── c++
│   │   ├── bananas.cpp
│   │   └── include
│   │   └── bananas.hpp
│   └── R
│   ├── bananas.R
│   └── wrapper.cpp
└── setup.R

And to demonstrate what is my problem you just run the setup.R.

I followed a standard tutorial, but I couldn't find any information of how I can load my BananasCPP class from the Bananas_cpp module inside my Bananas.R wrap function Bananas, while searching for days in the internet. This file does not appear in the namespace of the environment active inside the package, so I think this what should be tackled: "which commands I should add and where to expose my Bananas_cpp module inside the current namespace of the package".

Of course this is a reproducible that I made from a real problem I had.
Thanks a lot for your support!