as_cpp<Enum>

.gitignore

@@ -4,6 +4,8 @@ README.html
 .clangd/
 cpp11test/compile_commands.json
 cpp11test/src/Makevars
+cpp11test/src/*.o
+cpp11test/src/*.so
 compile_flags.txt
 inst/doc
 vignettes/*_cache

NEWS.md

@@ -1,5 +1,7 @@
 # cpp11 (development version)
 
+* `as_cpp<E>()` now allows enumeration `E` (#52, @bkietz)
+
 * `writable::logicals::operator=()` now allows C++ boolean values (#57, @romainfrancois)
 
 * `list::const_iterator::operator*()` added so iterators could be used on list objects (#60, @romainfrancois)

cpp11test/src/test-as.cpp

@@ -75,6 +75,19 @@ context("as_cpp-C++") {
     UNPROTECT(3);
   }
 
+  test_that("as_cpp<enum>(INTSEXP)") {
+    enum Response { YES, NO, MAYBE };
+    SEXP r = PROTECT(Rf_allocVector(INTSXP, 1));
+
+    for (Response e : {YES, NO, 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

@@ -71,6 +71,18 @@ is_integral<T> as_cpp(SEXP from) {
   return T();
 }
 
+template <typename E>
+using is_enum = typename std::enable_if<std::is_enum<E>::value, E>::type;
+
+template <typename E>
+is_enum<E> as_cpp(SEXP from) {
+  if (Rf_isInteger(from)) {
+    return static_cast<E>(as_cpp<typename std::underlying_type<E>::type>(from));
+  }
+
+  stop("Expected single integer value");
+}
+
 template <typename T>
 using is_logical =
     typename std::enable_if<std::is_same<typename std::decay<T>::type, bool>::value,