diff --git a/source/mijin/util/traits.hpp b/source/mijin/util/traits.hpp
index cb550f0..1699fbb 100644
--- a/source/mijin/util/traits.hpp
+++ b/source/mijin/util/traits.hpp
@@ -165,6 +165,23 @@ struct detect_or<TDefault, TOper, TArgs...>
 template<typename TDefault, template<typename...> typename TOper, typename... TArgs>
 using detect_or_t = detect_or<TDefault, TOper, TArgs...>::type;
 
+struct empty_type {};
+
+template<typename T, bool enable>
+struct optional_base
+{
+    using type = T;
+};
+
+template<typename T>
+struct optional_base<T, false>
+{
+    using type = empty_type;
+};
+
+template<typename T, bool enable>
+using optional_base_t = optional_base<T, enable>::type;
+
 //
 // public functions
 //