C++11 trailing return types not supported for exported functions

[klmr]

When using C++11 trailing return types on a function marked with [[Rcpp::export]], compilartion fails. Trailing return types work for non-exported functions.

Here’s an MWE (rcpptest.cpp):

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

#include <Rcpp.h>

auto impl() -> int { return 42; }

// [[Rcpp::export]]
auto test() -> int { return impl(); }

Rcpp::sourceCpp('rcpptest.cpp')

rcpptest.cpp:13:1: error: 'auto' return without trailing return type; deduced return types are a C++14 extension
auto test();
^
1 error generated.
make: *** [rcpptest.o] Error 1
clang++ -std=c++11 -I/usr/local/Cellar/r/3.3.2/R.framework/Resources/include -DNDEBUG  -I/usr/local/opt/gettext/include -I/usr/local/opt/readline/include -I/usr/local/opt/openssl/include -I/usr/local/include  -I"/Users/konrad/.R/packages/Rcpp/include" -I"/Users/konrad/tmp"   -fPIC  -g -O2 -c rcpptest.cpp -o rcpptest.o
Error in Rcpp::sourceCpp("rcpptest.cpp") :
  Error 1 occurred building shared library.

By changing the definition of test (but not impl!) to use conventional return types, the code compiles:

// [[Rcpp::export]]
int test() { return impl(); }

[jjallaire]

Good find. We're unlikely to fix this though as we have an ad-hoc parser for C++ that was developed some years ago. Modifying it for this alternate way of expressing return types carries cost and risk that IMO aren't warranted.

One related undertaking we've considered is to allow parsing to optionally use libclang (when available). That's not on the short term roadmap but would also remedy this issue.

[klmr]

I suspected as much from the error message.

👍 for libclang support, in the long run.

[marimeireles]

Any plans for implementing this?
Thanks.

[eddelbuettel]

No, I think that was addressed in the comments above from 2017 (indicating likely side effects to a core functionality) so I should probably just close this.

Or do you have any new insights to share?

[github-actions]

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