diff --git a/include/cppcore/conversion/enum.h b/include/cppcore/conversion/enum.h
index ee082b5..d9cc0ee 100644
--- a/include/cppcore/conversion/enum.h
+++ b/include/cppcore/conversion/enum.h
@@ -12,7 +12,7 @@
     namespace cppcore { \
     namespace __impl { \
     template<> \
-    struct enum_value_traits<enum> \
+    struct enum_value_traits<enum, void> \
     { \
         using enum_type              = enum; \
         using enum_value_pair_type   = std::pair<enum_type, std::string>; \
@@ -38,7 +38,7 @@ namespace cppcore
          *
          * @tparam T_enum   Enum type.
          */
-        template<typename T_enum>
+        template<typename T_enum, typename = void>
         struct enum_value_traits
         {
             using enum_type              = T_enum;
diff --git a/include/cppcore/conversion/enum.inl b/include/cppcore/conversion/enum.inl
index 6922639..15fd2ac 100644
--- a/include/cppcore/conversion/enum.inl
+++ b/include/cppcore/conversion/enum.inl
@@ -8,6 +8,15 @@ namespace cppcore
     namespace __impl
     {
 
+        /* enum_value_traits */
+
+        template<typename T_enum, typename T_enable>
+        decltype(auto) enum_value_traits<T_enum, T_enable>::get_enum_values()
+        {
+            static const auto value = enum_value_vector_type();
+            return value;
+        }
+
         /* enum_conversion_traits */
 
         template<typename T_enum, typename T_traits>
diff --git a/include/cppcore/conversion/string.inl b/include/cppcore/conversion/string.inl
index 8c3f739..51e2faa 100644
--- a/include/cppcore/conversion/string.inl
+++ b/include/cppcore/conversion/string.inl
@@ -159,6 +159,15 @@ namespace cppcore
                 { return std::string(v, N-1); }
         };
 
+        template<typename T>
+        struct op_to_string<T*, std::enable_if_t<std::is_same_v<std::decay_t<T>, char>>>
+        {
+            using value_type = T*;
+
+            inline std::string operator()(const value_type& v) const
+                { return std::string(v); }
+        };
+
         template<typename T>
         struct op_to_string<T, decltype(std::declval<T>().to_string(std::declval<std::ostream&>()), void())>
         {
diff --git a/include/cppcore/misc/exception.h b/include/cppcore/misc/exception.h
index e55075c..b113b7f 100644
--- a/include/cppcore/misc/exception.h
+++ b/include/cppcore/misc/exception.h
@@ -91,7 +91,7 @@ namespace cppcore
         /**
          * @brief Convert the exception to a string.
          */
-        inline std::string to_string() const;
+        inline const std::string& to_string() const;
 
         /**
          * @brief Get the message of the exception as c-string.
diff --git a/include/cppcore/misc/exception.inl b/include/cppcore/misc/exception.inl
index 258a406..84607a9 100644
--- a/include/cppcore/misc/exception.inl
+++ b/include/cppcore/misc/exception.inl
@@ -53,14 +53,14 @@ namespace cppcore
         return os.str();
     }
 
-    std::string exception::to_string() const
+    const std::string& exception::to_string() const
     {
         if (_msg_cache_empty)
         {
             _msg_cache      = print();
             _msg_cache_empty = false;
         }
-        return _msg_cache.c_str();
+        return _msg_cache;
     }
 
     const char* exception::what() const throw()