add detail/conversions/from_json.hpp

Makefile

@@ -7,7 +7,9 @@ SRCS = ${SRCDIR}/json.hpp \
 			 ${SRCDIR}/detail/macro_unscope.hpp \
 			 ${SRCDIR}/detail/meta.hpp \
 			 ${SRCDIR}/detail/exceptions.hpp \
-			 ${SRCDIR}/detail/value_t.hpp
+			 ${SRCDIR}/detail/value_t.hpp \
+			 ${SRCDIR}/detail/conversions/from_json.hpp
+
 
 
 

src/detail/meta.hpp

@@ -220,6 +220,16 @@ struct has_to_json
     static constexpr bool value = std::is_integral<decltype(detect(
                                       std::declval<typename BasicJsonType::template json_serializer<T, void>>()))>::value;
 };
+
+// taken from ranges-v3
+template<typename T>
+struct static_const
+{
+    static constexpr T value{};
+};
+
+template<typename T>
+constexpr T static_const<T>::value;
 }
 }