change APIVariant to class

HalideIR @ 0fe824d6

-Subproject commit bd94f8c8e41b46ae7ca69a3405aac7463a4e23d5
+Subproject commit 0fe824d680fe9c2ccbd874d4a80b26d92e65fbec

src/c_api/c_api_registry.h

@@ -44,7 +44,8 @@ inline Type String2Type(std::string s) {
 }
 
 /*! \brief Variant container for API calls */
-struct APIVariantValue {
+class APIVariantValue {
+ public:
   /*! \brief the type id */
   ArgVariantID type_id{kNull};
   /*! \brief shared pointer container */