handle enum with underlying type char (#74)

Co-authored-by: Benjamin Kietzman <[email protected]>

Author: romainfrancois

cpp11test/src/test-as.cpp

@@ -90,6 +90,19 @@ context("as_cpp-C++") {
     UNPROTECT(1);
   }
 
+  test_that("as_cpp<enum:char>(INTSEXP)") {
+    enum class Response: char { YES, NO, MAYBE };
+    SEXP r = PROTECT(Rf_allocVector(INTSXP, 1));
+
+    for (Response e : {Response::YES, Response::NO, Response::MAYBE, static_cast<Response>(42)}) {
+      INTEGER(r)[0] = static_cast<int>(e);
+      auto x = cpp11::as_cpp<Response>(r);
+      expect_true(x == e);
+    }
+
+    UNPROTECT(1);
+  }
+
   test_that("as_cpp<double>(REALSXP)") {
     SEXP r = PROTECT(Rf_allocVector(REALSXP, 1));
     REAL(r)[0] = 1.2;

inst/include/cpp11/as.hpp

@@ -96,7 +96,13 @@ enable_if_integral<T, T> as_cpp(SEXP from) {
 template <typename E>
 enable_if_enum<E, E> as_cpp(SEXP from) {
   if (Rf_isInteger(from)) {
-    return static_cast<E>(as_cpp<typename std::underlying_type<E>::type>(from));
+    using underlying_type = typename std::underlying_type<E>::type;
+    using int_type = typename std::conditional<
+      std::is_same<char, underlying_type>::value,
+      int, // as_cpp<char> would trigger undesired string conversions
+      underlying_type
+    >::type;
+    return static_cast<E>(as_cpp<int_type>(from));
   }
 
   stop("Expected single integer value");