Rcpp compile error: cannot convert List to SEXP - r

Question

If I adapt some working Rcpp code to put it into a class, it stops working.
Here is the working, non-class-based code:
#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
List test1_() {
Rcpp::NumericVector x = Rcpp::NumericVector::create(1.0);
return Rcpp::List::create(Rcpp::Named("x") = x);
}
But when I separate it into .cpp ...
// testlist.cpp
#include <Rcpp.h>
#include "testlist.h"
using namespace Rcpp;
// [[Rcpp::export]]
SEXP test2_() {
testlist a_testlist;
return a_testlist.test;
}
... and .h ...
// testlist.h
#ifndef TESTLIST_
#define TESTLIST_
#include <Rcpp.h>
class testlist {
public:
testlist() {}
Rcpp::List test() {
Rcpp::NumericVector x = Rcpp::NumericVector::create(1.0);
return Rcpp::List::create(Rcpp::Named("x") = x);
}
};
#endif
... then I get the following compilation error.
g++ -I/usr/include/R/ -DNDEBUG -D_FORTIFY_SOURCE=2 -I"/home/nacnudus/R/x86_64-pc-linux-gnu-library/3.3/Rcpp/include" -fpic -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -c RcppExports.cpp -o RcppExports.o
g++ -I/usr/include/R/ -DNDEBUG -D_FORTIFY_SOURCE=2 -I"/home/nacnudus/R/x86_64-pc-linux-gnu-library/3.3/Rcpp/include" -fpic -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -c testlist.cpp -o testlist.o
testlist.cpp: In function ‘Rcpp::List test2_()’:
testlist.cpp:8:21: error: cannot convert ‘testlist::test’ from type ‘Rcpp::List (testlist::)() {aka Rcpp::Vector<19> (testlist::)()}’ to type ‘Rcpp::List {aka Rcpp::Vector<19>}’
return a_testlist.test;
^~~~
make: *** [/usr/lib64/R/etc/Makeconf:141: testlist.o] Error 1
ERROR: compilation failed for package ‘testlist’
* removing ‘/tmp/RtmppNxPq5/devtools_install_f654fb60a32/testlist’
What am I doing wrong?

Answer 1

Simple typo:
return a_testlist.test;
Needs to be:
return a_testlist.test();
Though, you should consider reading the Rcpp-modules vignette to properly expose classes.