Does this support C++14?

[SteveBronder]

Sorry if this is a dumb question but is cpp11 safe to use when working with C++14/17 features?

[jimhester]

Yes, you just need to then set C++14 in your SystemRequirements field in the DESCRIPTION file.

[SteveBronder]

Cool beans!

[bgoodri]

Is it also possible to utilize later C++ standards at runtime with cpp_function, etc.? When I do (with version 0.2.4),

Sys.setenv(USE_CXX14 = 1)
library(cpp11)
cpp_function(quiet = FALSE, code = 
'
auto mean_cpp(doubles x) { // N.B. C++14 feature
   int n = x.size();
   double total = 0;
   for(double value : x) {
     total += value;
   }
   return total / n;
}
')

it seems to hardcode the C++11 standard despite setting the USE_CXX14 environmental variable because I get

g++-8 -std=gnu++11 -I"/home/ben/r-devel/include" -DNDEBUG -I/home/ben/r-devel/library/cpp11/include -I/usr/local/include -fpic -O3 -g0 -c /tmp/RtmpssLUTy/file1d022dac909f/src/code_4.cpp -o /tmp/RtmpssLUTy/file1d022dac909f/src/code_4.o
/tmp/RtmpssLUTy/file1d022dac909f/src/code_4.cpp:6:24: error: ‘mean_cpp’ function uses ‘auto’ type specifier without trailing return type
auto mean_cpp(doubles x) {
^
/tmp/RtmpssLUTy/file1d022dac909f/src/code_4.cpp:6:24: note: deduced return type only available with -std=c++14 or -std=gnu++14
make: *** [/home/ben/r-devel/etc/Makeconf:177: /tmp/RtmpssLUTy/file1d022dac909f/src/code_4.o] Error 1

And if I add -std=c++14 to my CXX11FLAGS in ~/.R/Makevars to force it to use the C++14 standard, the above gives me a compiler error:

g++-8 -std=gnu++11 -I"/home/ben/r-devel/include" -DNDEBUG -I/home/ben/r-devel/library/cpp11/include -I/usr/local/include -fpic -O3 -g0 -std=c++14 -c /tmp/Rtmpe1TeiZ/file1f5742959b81/src/code_0.cpp -o /tmp/Rtmpe1TeiZ/file1f5742959b81/src/code_0.o
g++-8 -std=gnu++11 -I"/home/ben/r-devel/include" -DNDEBUG -I/home/ben/r-devel/library/cpp11/include -I/usr/local/include -fpic -O3 -g0 -std=c++14 -c /tmp/Rtmpe1TeiZ/file1f5742959b81/src/cpp11.cpp -o /tmp/Rtmpe1TeiZ/file1f5742959b81/src/cpp11.o
/tmp/Rtmpe1TeiZ/file1f5742959b81/src/cpp11.cpp: In function ‘SEXPREC* _code_0_mean_cpp(SEXP)’:
/tmp/Rtmpe1TeiZ/file1f5742959b81/src/cpp11.cpp:7:77: error: use of ‘auto mean_cpp(cpp11::doubles)’ before deduction of ‘auto’
return cpp11::as_sexp(mean_cpp(cpp11::as_cpp<cpp11::decay_t>(x))); ^
make: *** [/home/ben/r-devel/etc/Makeconf:177: /tmp/Rtmpe1TeiZ/file1f5742959b81/src/cpp11.o] Error 1

[jimhester]

No, it is not possible to do this currently.

Really for any non-trivial usage it is expected that you are writing an R package and I would really encourage you to do so if you are not.

[bgoodri]

Thanks. We have a package that uses Rcpp at runtime, but I was hoping I could use cpp11 with the C++14 standard to reduce the peak memory consumption.

Do you mean specifically that it would not be easy to get the auto return type to work for exported functions or that it would not be easy to get C++14 to work at all with cpp_function?

[jimhester]

Ah I see. I added a cxx_std argument that will allow you to control this.

Note however that you still can't use auto return types for functions registered by [[cpp11::register]], however they can be used for all other functions without an issue.

[bgoodri]

Great! To make it feasible with cpp11 chunks in vignettes, could the cxx_std argument instead default to Sys.getenv("CXX_STD") and then have cxx_source internally map to "CXX11" if CXX_STD was unset?

[jimhester]

Sure