+ list::const_iterator::operator*

[romainfrancois]

modeled after r_vector<r_string>::const_iterator::operator*.

This would otherwise fail as *it would give a nullptr

cpp11::cpp_function('SEXP premier(cpp11::list x) {
  auto it = x.begin(); 
  return *it;
}', quiet = FALSE)
#> clang++ -mmacosx-version-min=10.13 -std=gnu++11 -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -I/Users/romainfrancois/.R/library/4.0/cpp11/include  -I/usr/local/include   -fPIC  -Wall -O3 -Wall -Wimplicit-int-float-conversion -c /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/Rtmp3hU7Um/file11df6d2e2e10/src/code_0.cpp -o /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/Rtmp3hU7Um/file11df6d2e2e10/src/code_0.o
#> clang++ -mmacosx-version-min=10.13 -std=gnu++11 -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -I/Users/romainfrancois/.R/library/4.0/cpp11/include  -I/usr/local/include   -fPIC  -Wall -O3 -Wall -Wimplicit-int-float-conversion -c /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/Rtmp3hU7Um/file11df6d2e2e10/src/cpp11.cpp -o /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/Rtmp3hU7Um/file11df6d2e2e10/src/cpp11.o
#> clang++ -mmacosx-version-min=10.13 -std=gnu++11 -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/Library/Frameworks/R.framework/Resources/lib -L/usr/local/lib -o /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/Rtmp3hU7Um/file11df6d2e2e10/src/code_0.so /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/Rtmp3hU7Um/file11df6d2e2e10/src/code_0.o /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/Rtmp3hU7Um/file11df6d2e2e10/src/cpp11.o -F/Library/Frameworks/R.framework/.. -framework R -Wl,-framework -Wl,CoreFoundation

premier(list(1, 1:10, letters))
#> [1] 1

^{Created on 2020-07-27 by the reprex package (v0.3.0.9001)}

[jimhester]

Could you add a test to https://github.com/r-lib/cpp11/blob/master/cpp11test/src/test-list.cpp that uses this overload, otherwise looks good to me.