diff --git a/include/pocketpy/codeobject.h b/include/pocketpy/codeobject.h
index 4b175114..5d782c46 100644
--- a/include/pocketpy/codeobject.h
+++ b/include/pocketpy/codeobject.h
@@ -47,6 +47,10 @@ struct CodeBlock {
         type(type), parent(parent), for_loop_depth(for_loop_depth), start(start), end(-1) {}
 };
 
+struct CodeObject;
+typedef shared_ptr<CodeObject> CodeObject_;
+struct FuncDecl;
+using FuncDecl_ = shared_ptr<FuncDecl>;
 
 struct CodeObjectSerializer{
     std::string buffer;
@@ -107,4 +111,98 @@ struct CodeObject {
     Str serialize(VM* vm) const;
 };
 
+struct FuncDecl {
+    struct KwArg {
+        int key;                // index in co->varnames
+        PyObject* value;        // default value
+    };
+    CodeObject_ code;           // code object of this function
+    pod_vector<int> args;       // indices in co->varnames
+    pod_vector<KwArg> kwargs;   // indices in co->varnames
+    int starred_arg = -1;       // index in co->varnames, -1 if no *arg
+    int starred_kwarg = -1;     // index in co->varnames, -1 if no **kwarg
+    bool nested = false;        // whether this function is nested
+
+    Str signature;              // signature of this function
+    Str docstring;              // docstring of this function
+    void _gc_mark() const;
+};
+
+struct NativeFunc {
+    NativeFuncC f;
+
+    // old style argc-based call
+    int argc;
+
+    // new style decl-based call
+    FuncDecl_ decl;
+
+    using UserData = char[32];
+    UserData _userdata;
+    bool _has_userdata;
+
+    template <typename T>
+    void set_userdata(T data) {
+        static_assert(std::is_trivially_copyable_v<T>);
+        static_assert(sizeof(T) <= sizeof(UserData));
+        if(_has_userdata) throw std::runtime_error("userdata already set");
+        _has_userdata = true;
+        memcpy(_userdata, &data, sizeof(T));
+    }
+
+    template <typename T>
+    T get_userdata() const {
+        static_assert(std::is_trivially_copyable_v<T>);
+        static_assert(sizeof(T) <= sizeof(UserData));
+#if PK_DEBUG_EXTRA_CHECK
+        if(!_has_userdata) throw std::runtime_error("userdata not set");
+#endif
+        return reinterpret_cast<const T&>(_userdata);
+    }
+    
+    NativeFunc(NativeFuncC f, int argc, bool method);
+    NativeFunc(NativeFuncC f, FuncDecl_ decl);
+
+    void check_size(VM* vm, ArgsView args) const;
+    PyObject* call(VM* vm, ArgsView args) const;
+};
+
+struct Function{
+    FuncDecl_ decl;
+    PyObject* _module;
+    NameDict_ _closure;
+};
+
+template<>
+struct Py_<Function> final: PyObject {
+    Function _value;
+    Py_(Type type, Function val): PyObject(type), _value(val) {
+        enable_instance_dict();
+    }
+    void _obj_gc_mark() override {
+        _value.decl->_gc_mark();
+        if(_value._module != nullptr) PK_OBJ_MARK(_value._module);
+        if(_value._closure != nullptr) gc_mark_namedict(*_value._closure);
+    }
+};
+
+template<>
+struct Py_<NativeFunc> final: PyObject {
+    NativeFunc _value;
+    Py_(Type type, NativeFunc val): PyObject(type), _value(val) {
+        enable_instance_dict();
+    }
+    void _obj_gc_mark() override {
+        if(_value.decl != nullptr){
+            _value.decl->_gc_mark();
+        }
+    }
+};
+
+template<typename T>
+T lambda_get_userdata(PyObject** p){
+    if(p[-1] != PY_NULL) return PK_OBJ_GET(NativeFunc, p[-1]).get_userdata<T>();
+    else return PK_OBJ_GET(NativeFunc, p[-2]).get_userdata<T>();
+}
+
 } // namespace pkpy
\ No newline at end of file
diff --git a/include/pocketpy/obj.h b/include/pocketpy/obj.h
index 391a4e88..00dc362f 100644
--- a/include/pocketpy/obj.h
+++ b/include/pocketpy/obj.h
@@ -6,9 +6,6 @@
 
 namespace pkpy {
     
-struct CodeObject;
-typedef shared_ptr<CodeObject> CodeObject_;
-
 struct Frame;
 class VM;
 
@@ -18,70 +15,6 @@ using NativeFuncC = std::function<PyObject*(VM*, ArgsView)>;
 typedef PyObject* (*NativeFuncC)(VM*, ArgsView);
 #endif
 
-struct FuncDecl {
-    struct KwArg {
-        int key;                // index in co->varnames
-        PyObject* value;        // default value
-    };
-    CodeObject_ code;           // code object of this function
-    pod_vector<int> args;       // indices in co->varnames
-    pod_vector<KwArg> kwargs;   // indices in co->varnames
-    int starred_arg = -1;       // index in co->varnames, -1 if no *arg
-    int starred_kwarg = -1;     // index in co->varnames, -1 if no **kwarg
-    bool nested = false;        // whether this function is nested
-
-    Str signature;              // signature of this function
-    Str docstring;              // docstring of this function
-    void _gc_mark() const;
-};
-
-using FuncDecl_ = shared_ptr<FuncDecl>;
-
-struct NativeFunc {
-    NativeFuncC f;
-
-    // old style argc-based call
-    int argc;
-
-    // new style decl-based call
-    FuncDecl_ decl;
-
-    using UserData = char[32];
-    UserData _userdata;
-    bool _has_userdata;
-
-    template <typename T>
-    void set_userdata(T data) {
-        static_assert(std::is_trivially_copyable_v<T>);
-        static_assert(sizeof(T) <= sizeof(UserData));
-        if(_has_userdata) throw std::runtime_error("userdata already set");
-        _has_userdata = true;
-        memcpy(_userdata, &data, sizeof(T));
-    }
-
-    template <typename T>
-    T get_userdata() const {
-        static_assert(std::is_trivially_copyable_v<T>);
-        static_assert(sizeof(T) <= sizeof(UserData));
-#if PK_DEBUG_EXTRA_CHECK
-        if(!_has_userdata) throw std::runtime_error("userdata not set");
-#endif
-        return reinterpret_cast<const T&>(_userdata);
-    }
-    
-    NativeFunc(NativeFuncC f, int argc, bool method);
-    NativeFunc(NativeFuncC f, FuncDecl_ decl);
-
-    void check_size(VM* vm, ArgsView args) const;
-    PyObject* call(VM* vm, ArgsView args) const;
-};
-
-struct Function{
-    FuncDecl_ decl;
-    PyObject* _module;
-    NameDict_ _closure;
-};
-
 struct BoundMethod {
     PyObject* self;
     PyObject* func;
@@ -365,32 +298,6 @@ struct Py_<Slice> final: PyObject {
     }
 };
 
-template<>
-struct Py_<Function> final: PyObject {
-    Function _value;
-    Py_(Type type, Function val): PyObject(type), _value(val) {
-        enable_instance_dict();
-    }
-    void _obj_gc_mark() override {
-        _value.decl->_gc_mark();
-        if(_value._module != nullptr) PK_OBJ_MARK(_value._module);
-        if(_value._closure != nullptr) gc_mark_namedict(*_value._closure);
-    }
-};
-
-template<>
-struct Py_<NativeFunc> final: PyObject {
-    NativeFunc _value;
-    Py_(Type type, NativeFunc val): PyObject(type), _value(val) {
-        enable_instance_dict();
-    }
-    void _obj_gc_mark() override {
-        if(_value.decl != nullptr){
-            _value.decl->_gc_mark();
-        }
-    }
-};
-
 template<>
 struct Py_<Super> final: PyObject {
     Super _value;
@@ -427,10 +334,4 @@ struct Py_<DummyModule> final: PyObject {
     void _obj_gc_mark() override {}
 };
 
-template<typename T>
-T lambda_get_userdata(PyObject** p){
-    if(p[-1] != PY_NULL) return PK_OBJ_GET(NativeFunc, p[-1]).get_userdata<T>();
-    else return PK_OBJ_GET(NativeFunc, p[-2]).get_userdata<T>();
-}
-
 }   // namespace pkpy
\ No newline at end of file
diff --git a/src/codeobject.cpp b/src/codeobject.cpp
index 2d7c03dd..95a8f3d4 100644
--- a/src/codeobject.cpp
+++ b/src/codeobject.cpp
@@ -154,4 +154,18 @@ void CodeObjectSerializer::write_code(VM* vm, const CodeObject* co){
     buffer += END;
 }
 
+    NativeFunc::NativeFunc(NativeFuncC f, int argc, bool method){
+        this->f = f;
+        this->argc = argc;
+        if(argc != -1) this->argc += (int)method;
+        _has_userdata = false;
+    }
+
+    NativeFunc::NativeFunc(NativeFuncC f, FuncDecl_ decl){
+        this->f = f;
+        this->argc = -1;
+        this->decl = decl;
+        _has_userdata = false;
+    }
+
 }   // namespace pkpy
\ No newline at end of file
diff --git a/src/obj.cpp b/src/obj.cpp
index a2d0eba7..8cb04ab1 100644
--- a/src/obj.cpp
+++ b/src/obj.cpp
@@ -1,21 +1,6 @@
 #include "pocketpy/obj.h"
 
 namespace pkpy{
-
-    NativeFunc::NativeFunc(NativeFuncC f, int argc, bool method){
-        this->f = f;
-        this->argc = argc;
-        if(argc != -1) this->argc += (int)method;
-        _has_userdata = false;
-    }
-
-    NativeFunc::NativeFunc(NativeFuncC f, FuncDecl_ decl){
-        this->f = f;
-        this->argc = -1;
-        this->decl = decl;
-        _has_userdata = false;
-    }
-
     PyObject::~PyObject() {
         if(_attr == nullptr) return;
         _attr->~NameDict();