diff --git a/src/cffi.h b/src/cffi.h
index 94966c6e..593b1cd2 100644
--- a/src/cffi.h
+++ b/src/cffi.h
@@ -5,7 +5,7 @@
 namespace pkpy {
 
 struct CType{
-    PY_CLASS(c, type_)
+    PY_CLASS(CType, c, type_)
 
     const char* name;       // must be a literal
     const int size;
@@ -16,7 +16,7 @@ struct CType{
         vm->bind_static_method<-1>(type, "__new__", CPP_NOT_IMPLEMENTED());
 
         vm->bind_method<0>(type, "__repr__", [](VM* vm, Args& args) {
-            CType& self = vm->_cast<CType>(args[0]);
+            CType& self = CAST(CType, args[0]);
             StrStream ss;
             ss << "<c._type '" << self.name << "' (" << self.size*8 << " bits)>";
             return VAR(ss.str());
@@ -51,7 +51,7 @@ constexpr int C_TYPE(const char name[]){
 #define C_TYPE_T(x) (kCTypes[C_TYPE(x)])
 
 struct Pointer{
-    PY_CLASS(c, ptr_)
+    PY_CLASS(Pointer, c, ptr_)
 
     void* ptr;
     CType ctype;       // base type
@@ -70,61 +70,61 @@ struct Pointer{
         vm->bind_static_method<-1>(type, "__new__", CPP_NOT_IMPLEMENTED());
 
         vm->bind_method<0>(type, "__repr__", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
+            Pointer& self = CAST(Pointer, args[0]);
             StrStream ss;
             ss << "<" << self.ctype.name << "* at " << (i64)self.ptr << ">";
             return VAR(ss.str());
         });
 
         vm->bind_method<1>(type, "__add__", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
-            return vm->new_object<Pointer>(self + CAST(i64, args[1]));
+            Pointer& self = CAST(Pointer, args[0]);
+            return VAR_T(Pointer, self + CAST(i64, args[1]));
         });
 
         vm->bind_method<1>(type, "__sub__", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
-            return vm->new_object<Pointer>(self - CAST_V(i64, args[1]));
+            Pointer& self = CAST(Pointer, args[0]);
+            return VAR_T(Pointer, self - CAST_V(i64, args[1]));
         });
 
         vm->bind_method<1>(type, "__eq__", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
-            Pointer& other = vm->_cast<Pointer>(args[1]);
+            Pointer& self = CAST(Pointer, args[0]);
+            Pointer& other = CAST(Pointer, args[1]);
             return VAR(self.ptr == other.ptr);
         });
 
         vm->bind_method<1>(type, "__ne__", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
-            Pointer& other = vm->_cast<Pointer>(args[1]);
+            Pointer& self = CAST(Pointer, args[0]);
+            Pointer& other = CAST(Pointer, args[1]);
             return VAR(self.ptr != other.ptr);
         });
 
         // https://docs.python.org/zh-cn/3/library/ctypes.html
         vm->bind_method<1>(type, "__getitem__", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
+            Pointer& self = CAST(Pointer, args[0]);
             i64 index = CAST_V(i64, args[1]);
             return (self+index).get(vm);
         });
 
         vm->bind_method<2>(type, "__setitem__", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
+            Pointer& self = CAST(Pointer, args[0]);
             i64 index = CAST_V(i64, args[1]);
             (self+index).set(vm, args[2]);
             return vm->None;
         });
 
         vm->bind_method<1>(type, "cast", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
-            CType& ctype = vm->_cast<CType>(args[1]);
-            return vm->new_object<Pointer>(self.ptr, ctype);
+            Pointer& self = CAST(Pointer, args[0]);
+            CType& ctype = CAST(CType, args[1]);
+            return VAR_T(Pointer, self.ptr, ctype);
         });
 
         vm->bind_method<0>(type, "get", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
+            Pointer& self = CAST(Pointer, args[0]);
             return self.get(vm);
         });
 
         vm->bind_method<1>(type, "set", [](VM* vm, Args& args) {
-            Pointer& self = vm->_cast<Pointer>(args[0]);
+            Pointer& self = CAST(Pointer, args[0]);
             self.set(vm, args[1]);
             return vm->None;
         });
@@ -155,7 +155,7 @@ struct Pointer{
             case C_TYPE("uint16_"): return VAR(ref<uint16_t>());
             case C_TYPE("uint32_"): return VAR(ref<uint32_t>());
             case C_TYPE("uint64_"): return VAR(ref<uint64_t>());
-            case C_TYPE("void_p_"): return vm->new_object<Pointer>(ref<void*>(), C_TYPE_T("void_"));
+            case C_TYPE("void_p_"): return VAR_T(Pointer, ref<void*>(), C_TYPE_T("void_"));
             // use macro here to do extension
             default: UNREACHABLE();
         }
@@ -178,7 +178,7 @@ struct Pointer{
             case C_TYPE("uint16_"): ref<uint16_t>() = CAST_V(i64, val); break;
             case C_TYPE("uint32_"): ref<uint32_t>() = CAST_V(i64, val); break;
             case C_TYPE("uint64_"): ref<uint64_t>() = CAST_V(i64, val); break;
-            case C_TYPE("void_p_"): ref<void*>() = vm->_cast<Pointer>(val).ptr; break;
+            case C_TYPE("void_p_"): ref<void*>() = CAST(Pointer, val).ptr; break;
             // use macro here to do extension
             default: UNREACHABLE();
         }
@@ -209,7 +209,7 @@ static const StructMetaInfo _Point2_info = {
 };
 
 struct Struct {
-    PY_CLASS(c, struct_)
+    PY_CLASS(Struct, c, struct_)
 
     const StructMetaInfo* info;
     int8_t* _data;      // store any `struct`
@@ -238,11 +238,11 @@ struct Struct {
 
     static void _register(VM* vm, PyVar mod, PyVar type){
         vm->bind_static_method<-1>(type, "__new__", [](VM* vm, Args& args) {
-            return vm->new_object<Struct>();
+            return VAR_T(Struct);
         });
 
         vm->bind_method<0>(type, "__repr__", [](VM* vm, Args& args) {
-            Struct& self = vm->_cast<Struct>(args[0]);
+            Struct& self = CAST(Struct, args[0]);
             StrStream ss;
             ss << self.info->name << "(" << ")";
             return VAR(ss.str());
@@ -252,41 +252,41 @@ struct Struct {
 
 void add_module_c(VM* vm){
     PyVar mod = vm->new_module("c");
-    PyVar ptr_t = vm->register_class<Pointer>(mod);
-    vm->register_class<CType>(mod);
-    vm->register_class<Struct>(mod);
+    PyVar ptr_t = Pointer::register_class(vm, mod);
+    CType::register_class(vm, mod);
+    Struct::register_class(vm, mod);
 
     for(int i=0; i<kCTypeCount; i++){
-        vm->setattr(mod, kCTypes[i].name, vm->new_object<CType>(kCTypes[i]));
+        vm->setattr(mod, kCTypes[i].name, VAR_T(CType, kCTypes[i]));
     }
-    vm->setattr(mod, "nullptr", vm->new_object<Pointer>(nullptr, C_TYPE_T("void_")));
+    vm->setattr(mod, "nullptr", VAR_T(Pointer, nullptr, C_TYPE_T("void_")));
 
     vm->bind_func<1>(mod, "malloc", [](VM* vm, Args& args) {
         i64 size = CAST_V(i64, args[0]);
-        return vm->new_object<Pointer>(malloc(size), C_TYPE_T("void_"));
+        return VAR_T(Pointer, malloc(size), C_TYPE_T("void_"));
     });
 
     vm->bind_func<1>(mod, "free", [](VM* vm, Args& args) {
-        Pointer& self = vm->_cast<Pointer>(args[0]);
+        Pointer& self = CAST(Pointer, args[0]);
         free(self.ptr);
         return vm->None;
     });
 
     vm->bind_func<1>(mod, "sizeof", [](VM* vm, Args& args) {
-        CType& ctype = vm->_cast<CType>(args[0]);
+        CType& ctype = CAST(CType, args[0]);
         return VAR(ctype.size);
     });
 
     vm->bind_func<3>(mod, "memcpy", [](VM* vm, Args& args) {
-        Pointer& dst = vm->_cast<Pointer>(args[0]);
-        Pointer& src = vm->_cast<Pointer>(args[1]);
+        Pointer& dst = CAST(Pointer, args[0]);
+        Pointer& src = CAST(Pointer, args[1]);
         i64 size = CAST_V(i64, args[2]);
         memcpy(dst.ptr, src.ptr, size);
         return vm->None;
     });
 
     vm->bind_func<3>(mod, "memset", [](VM* vm, Args& args) {
-        Pointer& dst = vm->_cast<Pointer>(args[0]);
+        Pointer& dst = CAST(Pointer, args[0]);
         i64 val = CAST_V(i64, args[1]);
         i64 size = CAST_V(i64, args[2]);
         memset(dst.ptr, (int)val, size);
@@ -296,10 +296,10 @@ void add_module_c(VM* vm){
     vm->bind_func<1>(mod, "strdup", [ptr_t](VM* vm, Args& args) {
         if(is_type(args[0], vm->tp_str)){
             const Str& s = CAST(Str, args[0]);
-            return vm->new_object<Pointer>(strdup(s.c_str()), C_TYPE_T("char_"));
+            return VAR_T(Pointer, strdup(s.c_str()), C_TYPE_T("char_"));
         }else if(is_type(args[0], OBJ_GET(Type, ptr_t))){
-            Pointer& p = vm->_cast<Pointer>(args[0]);
-            return vm->new_object<Pointer>(strdup(p.cast<char*>()), C_TYPE_T("char_"));
+            Pointer& p = CAST(Pointer, args[0]);
+            return VAR_T(Pointer, strdup(p.cast<char*>()), C_TYPE_T("char_"));
         }else{
             vm->TypeError("strdup() argument must be 'str' or 'char*'");
             return vm->None;
@@ -307,13 +307,13 @@ void add_module_c(VM* vm){
     });
 
     vm->bind_func<2>(mod, "strcmp", [](VM* vm, Args& args) {
-        Pointer& p1 = vm->_cast<Pointer>(args[0]);
-        Pointer& p2 = vm->_cast<Pointer>(args[1]);
+        Pointer& p1 = CAST(Pointer, args[0]);
+        Pointer& p2 = CAST(Pointer, args[1]);
         return VAR(strcmp(p1.cast<char*>(), p2.cast<char*>()));
     });
 
     vm->bind_func<1>(mod, "strlen", [](VM* vm, Args& args) {
-        Pointer& p = vm->_cast<Pointer>(args[0]);
+        Pointer& p = CAST(Pointer, args[0]);
         return VAR(strlen(p.cast<char*>()));
     });
 }
diff --git a/src/obj.h b/src/obj.h
index a9c1fcc8..52930f2b 100644
--- a/src/obj.h
+++ b/src/obj.h
@@ -149,14 +149,19 @@ inline bool is_float(const PyVar& obj) noexcept {
     return obj.is_tag_10();
 }
 
-#define PY_CLASS(mod, name) \
-    inline static Type _type(VM* vm) {  \
+#define PY_CLASS(T, mod, name) \
+    static Type _type(VM* vm) {  \
         static StrName __x0(#mod);      \
         static StrName __x1(#name);     \
-        return OBJ_GET(Type, vm->_modules[__x0]->attr(__x1));  \
-    } \
-    inline static const char* _mod() { return #mod; } \
-    inline static const char* _name() { return #name; }
+        return OBJ_GET(Type, vm->_modules[__x0]->attr(__x1));               \
+    }                                                                       \
+    static PyVar register_class(VM* vm, PyVar mod) {                        \
+        PyVar type = vm->new_type_object(mod, #name, vm->_t(vm->tp_object));\
+        if(OBJ_NAME(mod) != #mod) UNREACHABLE();                            \
+        T::_register(vm, mod, type);                                        \
+        type->attr()._try_perfect_rehash();                                 \
+        return type;                                                        \
+    }                                                                       
 
 union __8B {
     i64 _int;
@@ -165,16 +170,37 @@ union __8B {
     __8B(f64 val) : _float(val) {}
 };
 
+template <typename, typename = void> struct is_py_class : std::false_type {};
+template <typename T> struct is_py_class<T, std::void_t<decltype(T::_type)>> : std::true_type {};
+
 template<typename T>
 T py_cast_v(VM* vm, const PyVar& var) { UNREACHABLE(); }
 template<typename T>
 T _py_cast_v(VM* vm, const PyVar& var) { UNREACHABLE(); }
+
 template<typename T>
-T& py_cast(VM* vm, const PyVar& var) { UNREACHABLE(); }
+void _check_py_class(VM* vm, const PyVar& var);
+
 template<typename T>
-T& _py_cast(VM* vm, const PyVar& var) { UNREACHABLE(); }
+T& py_cast(VM* vm, const PyVar& obj) {
+    if constexpr(is_py_class<T>::value){
+        _check_py_class<T>(vm, obj);
+        return OBJ_GET(T, obj);
+    }else{
+        throw std::runtime_error("bad py_cast() call");
+    }
+}
+template<typename T>
+T& _py_cast(VM* vm, const PyVar& obj) {
+    if constexpr(is_py_class<T>::value){
+        return OBJ_GET(T, obj);
+    }else{
+        throw std::runtime_error("bad py_cast() call");
+    }
+}
 
 #define VAR(x) py_var(vm, x)
+#define VAR_T(T, ...) vm->new_object(T::_type(vm), T(__VA_ARGS__))
 #define CAST(T, x) py_cast<T>(vm, x)
 #define CAST_V(T, x) py_cast_v<T>(vm, x)
 #define _CAST(T, x) _py_cast<T>(vm, x)
diff --git a/src/pocketpy.h b/src/pocketpy.h
index 4fc2ab37..a453d489 100644
--- a/src/pocketpy.h
+++ b/src/pocketpy.h
@@ -611,7 +611,7 @@ void add_module_dis(VM* vm){
 }
 
 struct FileIO {
-    PY_CLASS(io, FileIO)
+    PY_CLASS(FileIO, io, FileIO)
 
     Str file;
     Str mode;
@@ -630,32 +630,32 @@ struct FileIO {
 
     static void _register(VM* vm, PyVar mod, PyVar type){
         vm->bind_static_method<2>(type, "__new__", [](VM* vm, Args& args){
-            return vm->new_object<FileIO>(
+            return VAR_T(FileIO, 
                 vm, CAST(Str, args[0]), CAST(Str, args[1])
             );
         });
 
         vm->bind_method<0>(type, "read", [](VM* vm, Args& args){
-            FileIO& io = vm->_cast<FileIO>(args[0]);
+            FileIO& io = CAST(FileIO, args[0]);
             std::string buffer;
             io._fs >> buffer;
             return VAR(buffer);
         });
 
         vm->bind_method<1>(type, "write", [](VM* vm, Args& args){
-            FileIO& io = vm->_cast<FileIO>(args[0]);
+            FileIO& io = CAST(FileIO, args[0]);
             io._fs << CAST(Str, args[1]);
             return vm->None;
         });
 
         vm->bind_method<0>(type, "close", [](VM* vm, Args& args){
-            FileIO& io = vm->_cast<FileIO>(args[0]);
+            FileIO& io = CAST(FileIO, args[0]);
             io._fs.close();
             return vm->None;
         });
 
         vm->bind_method<0>(type, "__exit__", [](VM* vm, Args& args){
-            FileIO& io = vm->_cast<FileIO>(args[0]);
+            FileIO& io = CAST(FileIO, args[0]);
             io._fs.close();
             return vm->None;
         });
@@ -665,7 +665,7 @@ struct FileIO {
 };
 void add_module_io(VM* vm){
     PyVar mod = vm->new_module("io");
-    PyVar type = vm->register_class<FileIO>(mod);
+    PyVar type = FileIO::register_class(vm, mod);
     vm->bind_builtin_func<2>("open", [type](VM* vm, const Args& args){
         return vm->call(type, args);
     });
@@ -674,7 +674,7 @@ void add_module_io(VM* vm){
 void add_module_os(VM* vm){}
 
 struct ReMatch {
-    PY_CLASS(re, Match)
+    PY_CLASS(ReMatch, re, Match)
 
     i64 start;
     i64 end;
@@ -683,16 +683,16 @@ struct ReMatch {
 
     static void _register(VM* vm, PyVar mod, PyVar type){
         vm->bind_method<-1>(type, "__init__", CPP_NOT_IMPLEMENTED());
-        vm->bind_method<0>(type, "start", CPP_LAMBDA(VAR(vm->_cast<ReMatch>(args[0]).start)));
-        vm->bind_method<0>(type, "end", CPP_LAMBDA(VAR(vm->_cast<ReMatch>(args[0]).end)));
+        vm->bind_method<0>(type, "start", CPP_LAMBDA(VAR(CAST(ReMatch, args[0]).start)));
+        vm->bind_method<0>(type, "end", CPP_LAMBDA(VAR(CAST(ReMatch, args[0]).end)));
 
         vm->bind_method<0>(type, "span", [](VM* vm, Args& args) {
-            auto& self = vm->_cast<ReMatch>(args[0]);
+            auto& self = CAST(ReMatch, args[0]);
             return VAR(two_args(VAR(self.start), VAR(self.end)));
         });
 
         vm->bind_method<1>(type, "group", [](VM* vm, Args& args) {
-            auto& self = vm->_cast<ReMatch>(args[0]);
+            auto& self = CAST(ReMatch, args[0]);
             int index = (int)CAST_V(i64, args[1]);
             index = vm->normalized_index(index, self.m.size());
             return VAR(self.m[index].str());
@@ -707,14 +707,14 @@ PyVar _regex_search(const Str& pattern, const Str& string, bool fromStart, VM* v
         if(fromStart && m.position() != 0) return vm->None;
         i64 start = string._to_u8_index(m.position());
         i64 end = string._to_u8_index(m.position() + m.length());
-        return vm->new_object<ReMatch>(start, end, m);
+        return VAR_T(ReMatch, start, end, m);
     }
     return vm->None;
 };
 
 void add_module_re(VM* vm){
     PyVar mod = vm->new_module("re");
-    vm->register_class<ReMatch>(mod);
+    ReMatch::register_class(vm, mod);
 
     vm->bind_func<2>(mod, "match", [](VM* vm, Args& args) {
         const Str& pattern = CAST(Str, args[0]);
diff --git a/src/vm.h b/src/vm.h
index a6325246..befb73d1 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -192,11 +192,6 @@ public:
         return make_sp<PyObject, Py_<RAW(T)>>(type, std::move(_value));
     }
 
-    template<typename T, typename... Args>
-    inline PyVar new_object(Args&&... args) {
-        return new_object(T::_type(this), T(std::forward<Args>(args)...));
-    }
-
     template<int ARGC>
     void bind_func(Str typeName, Str funcName, NativeFuncRaw fn) {
         bind_func<ARGC>(_types[typeName], funcName, fn);     
@@ -290,21 +285,6 @@ public:
         return _all_types[OBJ_GET(Type, _t(obj->type)).index];
     }
 
-    template<typename T>
-    PyVar register_class(PyVar mod){
-        PyVar type = new_type_object(mod, T::_name(), _t(tp_object));
-        if(OBJ_NAME(mod) != T::_mod()) UNREACHABLE();
-        T::_register(this, mod, type);
-        type->attr()._try_perfect_rehash();
-        return type;
-    }
-
-    template<typename T>
-    inline T& _cast(const PyVar& obj){
-        check_type(obj, T::_type(this));
-        return OBJ_GET(T, obj);
-    }
-
     ~VM() {
         if(!use_stdio){
             delete _stdout;
@@ -446,6 +426,11 @@ PyVar py_var(VM* vm, const char* val){
     return VAR(Str(val));
 }
 
+template<typename T>
+void _check_py_class(VM* vm, const PyVar& obj){
+    vm->check_type(obj, T::_type(vm));
+}
+
 PyVar VM::num_negated(const PyVar& obj){
     if (is_int(obj)){
         return VAR(-CAST_V(i64, obj));