diff --git a/src/obj.h b/src/obj.h
index 114f1707..5ad48eb1 100644
--- a/src/obj.h
+++ b/src/obj.h
@@ -13,16 +13,17 @@ class VM;
 
 typedef PyObject* (*NativeFuncC)(VM*, ArgsView);
 typedef std::function<PyObject*(VM*, ArgsView)> NativeFuncCpp;
-using NativeFuncRaw = std::variant<NativeFuncC, NativeFuncCpp>;
 
 typedef shared_ptr<CodeObject> CodeObject_;
 
 struct NativeFunc {
-    NativeFuncRaw f;
+    NativeFuncC f;
+    NativeFuncCpp f_cpp;
     int argc;       // DONOT include self
     bool method;
     
-    NativeFunc(NativeFuncRaw f, int argc, bool method) : f(f), argc(argc), method(method) {}
+    NativeFunc(NativeFuncC f, int argc, bool method) : f(f), argc(argc), method(method) {}
+    NativeFunc(NativeFuncCpp f, int argc, bool method) : f(nullptr), f_cpp(f), argc(argc), method(method) {}
     PyObject* operator()(VM* vm, ArgsView args) const;
 };
 
diff --git a/src/vm.h b/src/vm.h
index 074e6bb5..fc861b42 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -395,11 +395,8 @@ inline PyObject* NativeFunc::operator()(VM* vm, ArgsView args) const{
     if(argc != -1 && args_size != argc) {
         vm->TypeError(fmt("expected ", argc, " arguments, but got ", args_size));
     }
-    if(std::holds_alternative<NativeFuncC>(f)){
-        return std::get<NativeFuncC>(f)(vm, args);
-    }else{
-        return std::get<NativeFuncCpp>(f)(vm, args);
-    }
+    if(f != nullptr) return f(vm, args);
+    return f_cpp(vm, args);
 }
 
 inline void CodeObject::optimize(VM* vm){