added enum contains functoin

include/enum.hpp

@@ -53,6 +53,11 @@ template <enum_type E> constexpr auto is_empty(const E &value) -> bool {
   return std::to_underlying(value) == 0;
 }
 
+template <enum_type E>
+constexpr auto contains(const E &lhs, const E &rhs) -> bool {
+  return std::to_underlying(lhs & rhs) != 0;
+}
+
 } // namespace bitflag_operators
 
 using bitflag_operators::enum_type;