added !operator for enum classes

global.h

@@ -74,6 +74,17 @@ constexpr inline T operator ^ (T lhs, T rhs)
     return static_cast<T>(static_cast<int>(lhs) ^ static_cast<int>(rhs));
 }
 
+template <typename T>
+constexpr inline bool operator ! (T lhs)
+{
+
+    static_assert(std::is_enum<T>::value,
+                  "template parameter is not an enum type");
+
+    return !static_cast<bool>(lhs);
+}
+
+
 // TO DO need to testing. I am think this is does not work.
 //template <class IntegerType>
 //constexpr IntegerType static_mul(const char* str, unsigned char depth, unsigned char index = 0) noexcept {