From dbcc8c599119cfe8a61147a71e47210e3039f9e8 Mon Sep 17 00:00:00 2001
From: Romain Francois <romain@rstudio.com>
Date: Wed, 5 Aug 2020 12:23:05 +0200
Subject: [PATCH 1/2] handle enum with underlying type char

---
 cpp11test/src/test-as.cpp | 13 +++++++++++++
 inst/include/cpp11/as.hpp |  7 ++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/cpp11test/src/test-as.cpp b/cpp11test/src/test-as.cpp
index 9c65a689..b4e5d9cc 100644
--- a/cpp11test/src/test-as.cpp
+++ b/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;
diff --git a/inst/include/cpp11/as.hpp b/inst/include/cpp11/as.hpp
index bcadfc57..d1cddac2 100644
--- a/inst/include/cpp11/as.hpp
+++ b/inst/include/cpp11/as.hpp
@@ -96,7 +96,12 @@ 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 Type = typename std::conditional<
+      std::is_same<char, typename std::underlying_type<E>::type>::value,
+      int,
+      typename std::underlying_type<E>::type
+    >::type;
+    return static_cast<E>(as_cpp<Type>(from));
   }
 
   stop("Expected single integer value");

From a451f4ba569dcf9f435dc512a0332971974f5e95 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Romain=20Fran=C3=A7ois?= <romain@rstudio.com>
Date: Thu, 6 Aug 2020 14:56:57 +0200
Subject: [PATCH 2/2] Update inst/include/cpp11/as.hpp

Co-authored-by: Benjamin Kietzman <bengilgit@gmail.com>
---
 inst/include/cpp11/as.hpp | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/inst/include/cpp11/as.hpp b/inst/include/cpp11/as.hpp
index d1cddac2..3523f240 100644
--- a/inst/include/cpp11/as.hpp
+++ b/inst/include/cpp11/as.hpp
@@ -96,12 +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)) {
-    using Type = typename std::conditional<
-      std::is_same<char, typename std::underlying_type<E>::type>::value,
-      int,
-      typename std::underlying_type<E>::type
+    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<Type>(from));
+    return static_cast<E>(as_cpp<int_type>(from));
   }
 
   stop("Expected single integer value");