replace constructor by from/to_json: unscoped enum types

this also means that one can do: j.get<unscoped_enum>();

src/json.hpp

@@ -432,7 +432,6 @@ template <typename T, typename BasicJson>
 struct is_compatible_basic_json_type
 {
     static auto constexpr value =
-        is_unscoped_enum<T>::value or
         std::is_same<T, BasicJson>::value or
         is_compatible_array_type<BasicJson, T>::value or
         is_compatible_object_type<typename BasicJson::object_t, T>::value;
@@ -569,6 +568,13 @@ void to_json(Json &j, CompatibleNumberIntegerType val) noexcept
   external_constructor<value_t::number_integer>::construct(j, val);
 }
 
+template <typename Json, typename UnscopedEnumType,
+          enable_if_t<is_unscoped_enum<UnscopedEnumType>::value, int> = 0>
+void to_json(Json &j, UnscopedEnumType e)
+{
+  external_constructor<value_t::number_integer>::construct(j, e);
+}
+
 template <typename Json>
 void from_json(Json const& j, typename Json::boolean_t& b)
 {
@@ -603,6 +609,15 @@ void from_json(Json const& j, typename Json::number_integer_t& val)
   get_arithmetic_value(j, val);
 }
 
+template <typename Json, typename UnscopedEnumType,
+          enable_if_t<is_unscoped_enum<UnscopedEnumType>::value, int> = 0>
+void from_json(Json const &j, UnscopedEnumType& e)
+{
+  typename std::underlying_type<UnscopedEnumType>::type val = e;
+  get_arithmetic_value(j, val);
+  e = static_cast<UnscopedEnumType>(val);
+}
+
 // overload for arithmetic types, not chosen for basic_json template arguments (BooleanType, etc..)
 //
 // note: Is it really necessary to provide explicit overloads for boolean_t etc..
@@ -1848,15 +1863,6 @@ class basic_json
         JSONSerializer<uncvref_t<T>>::to_json(*this, std::forward<T>(val));
     }
 
-    // Constructor for unscoped enums (not enum classes)
-    template <typename T, enable_if_t<is_unscoped_enum<T>::value, int> = 0>
-    basic_json(T val) noexcept
-        : m_type(value_t::number_integer),
-          m_value(static_cast<number_integer_t>(val))
-    {
-        assert_invariant();
-    }
-
     /*!
     @brief create a container (array or object) from an initializer list
 

src/json.hpp.re2c

@@ -432,7 +432,6 @@ template <typename T, typename BasicJson>
 struct is_compatible_basic_json_type
 {
     static auto constexpr value =
-        is_unscoped_enum<T>::value or
         std::is_same<T, BasicJson>::value or
         is_compatible_array_type<BasicJson, T>::value or
         is_compatible_object_type<typename BasicJson::object_t, T>::value;
@@ -569,6 +568,13 @@ void to_json(Json &j, CompatibleNumberIntegerType val) noexcept
   external_constructor<value_t::number_integer>::construct(j, val);
 }
 
+template <typename Json, typename UnscopedEnumType,
+          enable_if_t<is_unscoped_enum<UnscopedEnumType>::value, int> = 0>
+void to_json(Json &j, UnscopedEnumType e)
+{
+  external_constructor<value_t::number_integer>::construct(j, e);
+}
+
 template <typename Json>
 void from_json(Json const& j, typename Json::boolean_t& b)
 {
@@ -603,6 +609,15 @@ void from_json(Json const& j, typename Json::number_integer_t& val)
   get_arithmetic_value(j, val);
 }
 
+template <typename Json, typename UnscopedEnumType,
+          enable_if_t<is_unscoped_enum<UnscopedEnumType>::value, int> = 0>
+void from_json(Json const &j, UnscopedEnumType& e)
+{
+  typename std::underlying_type<UnscopedEnumType>::type val = e;
+  get_arithmetic_value(j, val);
+  e = static_cast<UnscopedEnumType>(val);
+}
+
 // overload for arithmetic types, not chosen for basic_json template arguments (BooleanType, etc..)
 //
 // note: Is it really necessary to provide explicit overloads for boolean_t etc..
@@ -1849,15 +1864,6 @@ class basic_json
         JSONSerializer<uncvref_t<T>>::to_json(*this, std::forward<T>(val));
     }
 
-    // Constructor for unscoped enums (not enum classes)
-    template <typename T, enable_if_t<is_unscoped_enum<T>::value, int> = 0>
-    basic_json(T val) noexcept
-        : m_type(value_t::number_integer),
-          m_value(static_cast<number_integer_t>(val))
-    {
-        assert_invariant();
-    }
-
     /*!
     @brief create a container (array or object) from an initializer list
 

test/src/unit-regression.cpp

@@ -63,10 +63,18 @@ TEST_CASE("regression tests")
 
     SECTION("pull request #71 - handle enum type")
     {
-        enum { t = 0 };
+        enum { t = 0 , u = 1};
         json j = json::array();
         j.push_back(t);
 
+        // maybe this is not the place to test this?
+        json j2 = u;
+
+        auto anon_enum_value = j2.get<decltype(u)>();
+        CHECK(u == anon_enum_value);
+
+        static_assert(std::is_same<decltype(anon_enum_value), decltype(u)>::value, "");
+
         j.push_back(json::object(
         {
             {"game_type", t}