enum with underlying type: char

[romainfrancois]

cpp11::cpp_source(code = '
#include <cpp11.hpp>

enum class Color : char { red, green = 20, blue };

[[cpp11::register]]
void fun(SEXP value) {
  cpp11::as_cpp<Color>(value);
}

', 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/RtmpzSpGdd/filef6b4538517d5/src/code_0.cpp -o /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/RtmpzSpGdd/filef6b4538517d5/src/code_0.o
#> In file included from /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/RtmpzSpGdd/filef6b4538517d5/src/code_0.cpp:2:
#> In file included from /Users/romainfrancois/.R/library/4.0/cpp11/include/cpp11.hpp:5:
#> /Users/romainfrancois/.R/library/4.0/cpp11/include/cpp11/as.hpp:80:27: error: call to function 'as_cpp' that is neither visible in the template definition nor found by argument-dependent lookup
#>     return static_cast<E>(as_cpp<typename std::underlying_type<E>::type>(from));
#>                           ^
#> /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/RtmpzSpGdd/filef6b4538517d5/src/code_0.cpp:8:10: note: in instantiation of function template specialization 'cpp11::as_cpp<Color>' requested here
#>   cpp11::as_cpp<Color>(value);
#>          ^
#> /Users/romainfrancois/.R/library/4.0/cpp11/include/cpp11/as.hpp:143:12: note: 'as_cpp' should be declared prior to the call site or in the global namespace
#> is_char<T> as_cpp(SEXP from) {
#>            ^
#> 1 error generated.
#> make: *** [/private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/RtmpzSpGdd/filef6b4538517d5/src/code_0.o] Error 1
#> Error in dyn.load(shared_lib, local = TRUE, now = TRUE): unable to load shared object '/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T//RtmpzSpGdd/filef6b4538517d5/src/code_0.so':
#>   dlopen(/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T//RtmpzSpGdd/filef6b4538517d5/src/code_0.so, 6): image not found
fun(0L)
#> Error in .Call("_code_0_fun", value, PACKAGE = "code_0"): "_code_0_fun" not available for .Call() for package "code_0"

^{Created on 2020-08-05 by the reprex package (v0.3.0.9001)}