From af9b21151ca704414ff82156e1a7eca98e3e62b1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Th=C3=A9o=20DELRIEU?= <delrieutheo@gmail.com>
Date: Sun, 2 Apr 2017 13:10:15 +0200
Subject: [PATCH] add enum class default conversions

---
 src/json.hpp                  | 25 ++++++++++---------------
 src/json.hpp.re2c             | 25 ++++++++++---------------
 test/src/unit-conversions.cpp |  9 +++++++++
 3 files changed, 29 insertions(+), 30 deletions(-)

diff --git a/src/json.hpp b/src/json.hpp
index 90a48538a..5df1bacc4 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -454,12 +454,6 @@ using enable_if_t = typename std::enable_if<B, T>::type;
 template<typename T>
 using uncvref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
 
-// taken from http://stackoverflow.com/a/26936864/266378
-template<typename T>
-using is_unscoped_enum =
-    std::integral_constant<bool, std::is_convertible<T, int>::value and
-    std::is_enum<T>::value>;
-
 /*
 Implementation of two C++17 constructs: conjunction, negation. This is needed
 to avoid evaluating all the traits in a condition
@@ -818,11 +812,12 @@ void to_json(BasicJsonType& j, CompatibleNumberIntegerType val) noexcept
     external_constructor<value_t::number_integer>::construct(j, static_cast<typename BasicJsonType::number_integer_t>(val));
 }
 
-template<typename BasicJsonType, typename UnscopedEnumType,
-         enable_if_t<is_unscoped_enum<UnscopedEnumType>::value, int> = 0>
-void to_json(BasicJsonType& j, UnscopedEnumType e) noexcept
+template<typename BasicJsonType, typename EnumType,
+         enable_if_t<std::is_enum<EnumType>::value, int> = 0>
+void to_json(BasicJsonType& j, EnumType e) noexcept
 {
-    external_constructor<value_t::number_integer>::construct(j, e);
+    using underlying_type = typename std::underlying_type<EnumType>::type;
+    external_constructor<value_t::number_integer>::construct(j, static_cast<underlying_type>(e));
 }
 
 template<typename BasicJsonType>
@@ -937,13 +932,13 @@ void from_json(const BasicJsonType& j, typename BasicJsonType::number_integer_t&
     get_arithmetic_value(j, val);
 }
 
-template<typename BasicJsonType, typename UnscopedEnumType,
-         enable_if_t<is_unscoped_enum<UnscopedEnumType>::value, int> = 0>
-void from_json(const BasicJsonType& j, UnscopedEnumType& e)
+template<typename BasicJsonType, typename EnumType,
+         enable_if_t<std::is_enum<EnumType>::value, int> = 0>
+void from_json(const BasicJsonType& j, EnumType& e)
 {
-    typename std::underlying_type<UnscopedEnumType>::type val;
+    typename std::underlying_type<EnumType>::type val;
     get_arithmetic_value(j, val);
-    e = static_cast<UnscopedEnumType>(val);
+    e = static_cast<EnumType>(val);
 }
 
 template<typename BasicJsonType>
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index d88830b9e..da503495d 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -454,12 +454,6 @@ using enable_if_t = typename std::enable_if<B, T>::type;
 template<typename T>
 using uncvref_t = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
 
-// taken from http://stackoverflow.com/a/26936864/266378
-template<typename T>
-using is_unscoped_enum =
-    std::integral_constant<bool, std::is_convertible<T, int>::value and
-    std::is_enum<T>::value>;
-
 /*
 Implementation of two C++17 constructs: conjunction, negation. This is needed
 to avoid evaluating all the traits in a condition
@@ -818,11 +812,12 @@ void to_json(BasicJsonType& j, CompatibleNumberIntegerType val) noexcept
     external_constructor<value_t::number_integer>::construct(j, static_cast<typename BasicJsonType::number_integer_t>(val));
 }
 
-template<typename BasicJsonType, typename UnscopedEnumType,
-         enable_if_t<is_unscoped_enum<UnscopedEnumType>::value, int> = 0>
-void to_json(BasicJsonType& j, UnscopedEnumType e) noexcept
+template<typename BasicJsonType, typename EnumType,
+         enable_if_t<std::is_enum<EnumType>::value, int> = 0>
+void to_json(BasicJsonType& j, EnumType e) noexcept
 {
-    external_constructor<value_t::number_integer>::construct(j, e);
+    using underlying_type = typename std::underlying_type<EnumType>::type;
+    external_constructor<value_t::number_integer>::construct(j, static_cast<underlying_type>(e));
 }
 
 template<typename BasicJsonType>
@@ -937,13 +932,13 @@ void from_json(const BasicJsonType& j, typename BasicJsonType::number_integer_t&
     get_arithmetic_value(j, val);
 }
 
-template<typename BasicJsonType, typename UnscopedEnumType,
-         enable_if_t<is_unscoped_enum<UnscopedEnumType>::value, int> = 0>
-void from_json(const BasicJsonType& j, UnscopedEnumType& e)
+template<typename BasicJsonType, typename EnumType,
+         enable_if_t<std::is_enum<EnumType>::value, int> = 0>
+void from_json(const BasicJsonType& j, EnumType& e)
 {
-    typename std::underlying_type<UnscopedEnumType>::type val;
+    typename std::underlying_type<EnumType>::type val;
     get_arithmetic_value(j, val);
-    e = static_cast<UnscopedEnumType>(val);
+    e = static_cast<EnumType>(val);
 }
 
 template<typename BasicJsonType>
diff --git a/test/src/unit-conversions.cpp b/test/src/unit-conversions.cpp
index 59969bf9d..0940ec51e 100644
--- a/test/src/unit-conversions.cpp
+++ b/test/src/unit-conversions.cpp
@@ -917,6 +917,15 @@ TEST_CASE("value conversion")
         }
     }
 
+    SECTION("get an enum")
+    {
+        enum c_enum { value_1, value_2 };
+        enum class cpp_enum { value_1, value_2 };
+
+        CHECK(json(value_1).get<c_enum>() == value_1);
+        CHECK(json(cpp_enum::value_1).get<cpp_enum>() == cpp_enum::value_1);
+    }
+
     SECTION("more involved conversions")
     {
         SECTION("object-like STL containers")