diff --git a/include/pybind11/internal/builtins.h b/include/pybind11/internal/builtins.h
new file mode 100644
index 00000000..2dadf0b1
--- /dev/null
+++ b/include/pybind11/internal/builtins.h
@@ -0,0 +1,117 @@
+#pragma once
+
+#include "types.h"
+
+namespace pybind11 {
+    inline void exec(const char* code, handle global = {}, handle local = {}) {
+        vm->py_exec(code, global.ptr(), local.ptr());
+    }
+
+    // wrapper for builtin functions in Python
+    inline bool hasattr(const handle& obj, const handle& name) {
+        auto& key = _builtin_cast<pkpy::Str>(name);
+        return vm->getattr(obj.ptr(), key, false) != nullptr;
+    }
+
+    inline bool hasattr(const handle& obj, const char* name) {
+        return vm->getattr(obj.ptr(), name, false) != nullptr;
+    }
+
+    inline void delattr(const handle& obj, const handle& name) {
+        auto& key = _builtin_cast<pkpy::Str>(name);
+        vm->delattr(obj.ptr(), key);
+    }
+
+    inline void delattr(const handle& obj, const char* name) { vm->delattr(obj.ptr(), name); }
+
+    inline object getattr(const handle& obj, const handle& name) {
+        auto& key = _builtin_cast<pkpy::Str>(name);
+        return reinterpret_borrow<object>(vm->getattr(obj.ptr(), key));
+    }
+
+    inline object getattr(const handle& obj, const char* name) {
+        return reinterpret_borrow<object>(vm->getattr(obj.ptr(), name));
+    }
+
+    inline object getattr(const handle& obj, const handle& name, const handle& default_) {
+        if(!hasattr(obj, name)) {
+            return reinterpret_borrow<object>(default_);
+        }
+        return getattr(obj, name);
+    }
+
+    inline object getattr(const handle& obj, const char* name, const handle& default_) {
+        if(!hasattr(obj, name)) {
+            return reinterpret_borrow<object>(default_);
+        }
+        return getattr(obj, name);
+    }
+
+    inline void setattr(const handle& obj, const handle& name, const handle& value) {
+        auto& key = _builtin_cast<pkpy::Str>(name);
+        vm->setattr(obj.ptr(), key, value.ptr());
+    }
+
+    inline void setattr(const handle& obj, const char* name, const handle& value) {
+        vm->setattr(obj.ptr(), name, value.ptr());
+    }
+
+    template <typename T>
+    inline bool isinstance(const handle& obj) {
+        pkpy::Type cls = _builtin_cast<pkpy::Type>(type::handle_of<T>().ptr());
+        return vm->isinstance(obj.ptr(), cls);
+    }
+
+    template <>
+    inline bool isinstance<handle>(const handle&) = delete;
+
+    template <>
+    inline bool isinstance<iterable>(const handle& obj) {
+        return hasattr(obj, "__iter__");
+    }
+
+    template <>
+    inline bool isinstance<iterator>(const handle& obj) {
+        return hasattr(obj, "__iter__") && hasattr(obj, "__next__");
+    }
+
+    inline bool isinstance(const handle& obj, const handle& type) {
+        return vm->isinstance(obj.ptr(), _builtin_cast<pkpy::Type>(type));
+    }
+
+    inline int64_t hash(const handle& obj) { return vm->py_hash(obj.ptr()); }
+
+    template <typename T, typename SFINAE = void>
+    struct type_caster;
+
+    template <typename T>
+    handle _cast(T&& value,
+                 return_value_policy policy = return_value_policy::automatic_reference,
+                 handle parent = handle()) {
+        using U = std::remove_pointer_t<std::remove_cv_t<std::remove_reference_t<T>>>;
+        return type_caster<U>::cast(std::forward<T>(value), policy, parent);
+    }
+
+    template <typename T>
+    object cast(T&& value,
+                return_value_policy policy = return_value_policy::automatic_reference,
+                handle parent = handle()) {
+        return reinterpret_borrow<object>(_cast(std::forward<T>(value), policy, parent));
+    }
+
+    template <typename T>
+    T cast(handle obj, bool convert = false) {
+        using Caster =
+            type_caster<std::remove_pointer_t<std::remove_cv_t<std::remove_reference_t<T>>>>;
+        Caster caster;
+
+        if(caster.load(obj, convert)) {
+            if constexpr(std::is_rvalue_reference_v<T>) {
+                return std::move(caster.value);
+            } else {
+                return caster.value;
+            }
+        }
+        throw std::runtime_error("Unable to cast Python instance to C++ type");
+    }
+}  // namespace pybind11
diff --git a/include/pybind11/internal/cast.h b/include/pybind11/internal/cast.h
new file mode 100644
index 00000000..f6cdc320
--- /dev/null
+++ b/include/pybind11/internal/cast.h
@@ -0,0 +1,173 @@
+#pragma once
+
+#include "instance.h"
+#include "builtins.h"
+#include "type_traits.h"
+
+namespace pybind11 {
+
+    using pkpy::is_floating_point_v;
+    using pkpy::is_integral_v;
+
+    template <typename T>
+    constexpr inline bool is_string_v =
+        std::is_same_v<T, char*> || std::is_same_v<T, const char*> ||
+        std::is_same_v<T, std::string> || std::is_same_v<T, std::string_view>;
+
+    template <typename T>
+    constexpr bool is_pyobject_v = std::is_base_of_v<handle, T>;
+
+    template <typename T, typename>
+    struct type_caster;
+
+    template <>
+    struct type_caster<bool> {
+        bool value;
+
+        bool load(const handle& src, bool) {
+            if(isinstance<pybind11::bool_>(src)) {
+                value = pkpy::_py_cast<bool>(vm, src.ptr());
+                return true;
+            }
+
+            return false;
+        }
+
+        static handle cast(bool src, return_value_policy, handle) {
+            return src ? vm->True : vm->False;
+        }
+    };
+
+    template <typename T>
+    struct type_caster<T, std::enable_if_t<is_integral_v<T>>> {
+        T value;
+
+        bool load(const handle& src, bool convert) {
+            if(isinstance<pybind11::int_>(src)) {
+                value = pkpy::_py_cast<T>(vm, src.ptr());
+                return true;
+            }
+
+            return false;
+        }
+
+        static handle cast(T src, return_value_policy, handle) { return pkpy::py_var(vm, src); }
+    };
+
+    template <typename T>
+    struct type_caster<T, std::enable_if_t<is_floating_point_v<T>>> {
+        T value;
+
+        bool load(const handle& src, bool convert) {
+            if(isinstance<pybind11::float_>(src)) {
+                value = pkpy::_py_cast<T>(vm, src.ptr());
+                return true;
+            }
+
+            if(convert && isinstance<pybind11::int_>(src)) {
+                value = pkpy::_py_cast<int64_t>(vm, src.ptr());
+                return true;
+            }
+
+            return false;
+        }
+
+        static handle cast(T src, return_value_policy, handle) { return pkpy::py_var(vm, src); }
+    };
+
+    template <typename T>
+    struct type_caster<T, std::enable_if_t<is_string_v<T>>> {
+        T value;
+
+        bool load(const handle& src, bool) {
+            if(isinstance<pybind11::str>(src)) {
+                // FIXME: support other kinds of string
+                value = pkpy::_py_cast<std::string>(vm, src.ptr());
+                return true;
+            }
+
+            return false;
+        }
+
+        static handle cast(const std::string& src, return_value_policy, handle) {
+            return pkpy::py_var(vm, src);
+        }
+    };
+
+    template <typename T>
+    struct type_caster<T, std::enable_if_t<is_pyobject_v<T>>> {
+        T value;
+
+        bool load(const handle& src, bool) {
+            if(isinstance<T>(src)) {
+                value = reinterpret_borrow<T>(src);
+                return true;
+            }
+
+            return false;
+        }
+
+        template <typename U>
+        static handle cast(U&& src, return_value_policy, handle) {
+            return std::forward<U>(src);
+        }
+    };
+
+    template <typename T, typename>
+    struct type_caster {
+        value_wrapper<T> value;
+
+        using underlying_type = std::remove_pointer_t<decltype(value.pointer)>;
+
+        bool load(handle src, bool convert) {
+            if(isinstance<underlying_type>(src)) {
+                auto& i = _builtin_cast<instance>(src);
+                value.pointer = &i.cast<underlying_type>();
+                return true;
+            }
+
+            return false;
+        }
+
+        template <typename U>
+        static handle cast(U&& value, return_value_policy policy, const handle& parent = handle()) {
+            // TODO: support implicit cast
+            const auto& info = typeid(underlying_type);
+            bool existed = vm->_cxx_typeid_map.find(info) != vm->_cxx_typeid_map.end();
+            if(existed) {
+                auto type = vm->_cxx_typeid_map[info];
+                return instance::create(std::forward<U>(value), type, policy, parent.ptr());
+            }
+            vm->TypeError("type not registered");
+        }
+    };
+
+    template <typename T>
+    struct type_caster<T, std::enable_if_t<std::is_pointer_v<T> || std::is_reference_v<T>>> {
+        using underlying = std::conditional_t<std::is_pointer_v<T>,
+                                              std::remove_pointer_t<T>,
+                                              std::remove_reference_t<T>>;
+
+        struct wrapper {
+            type_caster<underlying> caster;
+
+            operator T () {
+                if constexpr(std::is_pointer_v<T>) {
+                    return caster.value.pointer;
+                } else {
+                    return caster.value;
+                }
+            }
+        };
+
+        wrapper value;
+
+        bool load(const handle& src, bool convert) { return value.caster.load(src, convert); }
+
+        template <typename U>
+        static handle cast(U&& value, return_value_policy policy, const handle& parent) {
+            return type_caster<underlying>::cast(std::forward<U>(value), policy, parent);
+        }
+    };
+}  // namespace pybind11
+
diff --git a/include/pybind11/internal/class.h b/include/pybind11/internal/class.h
new file mode 100644
index 00000000..6adb892c
--- /dev/null
+++ b/include/pybind11/internal/class.h
@@ -0,0 +1,184 @@
+#pragma once
+
+#include "cpp_function.h"
+
+namespace pybind11 {
+
+    class module : public object {
+
+    public:
+        using object::object;
+
+        static module import(const char* name) {
+            if(name == std::string_view{"__main__"}) {
+                return module{vm->_main, true};
+            } else {
+                return module{vm->py_import(name, false), true};
+            }
+        }
+    };
+
+    // TODO:
+    // 1. inheritance
+    // 2. virtual function
+    // 3. factory function
+
+    template <typename T, typename... Others>
+    class class_ : public type {
+    public:
+        using type::type;
+
+        template <typename... Args>
+        class_(const handle& scope, const char* name, Args&&... args) :
+            type(vm->new_type_object(scope.ptr(),
+                                     name,
+                                     vm->tp_object,
+                                     false,
+                                     pkpy::PyTypeInfo::Vt::get<instance>()),
+                 true) {
+            pkpy::PyVar mod = scope.ptr();
+            mod->attr().set(name, m_ptr);
+            vm->_cxx_typeid_map[typeid(T)] = _builtin_cast<pkpy::Type>(m_ptr);
+            vm->bind_func(m_ptr, "__new__", -1, [](pkpy::VM* vm, pkpy::ArgsView args) {
+                auto cls = _builtin_cast<pkpy::Type>(args[0]);
+                return instance::create<T>(cls);
+            });
+        }
+
+        /// bind constructor
+        template <typename... Args, typename... Extra>
+        class_& def(init<Args...>, const Extra&... extra) {
+            if constexpr(!std::is_constructible_v<T, Args...>) {
+                static_assert(std::is_constructible_v<T, Args...>, "Invalid constructor arguments");
+            } else {
+                bind_function(
+                    *this,
+                    "__init__",
+                    [](T* self, Args... args) { new (self) T(args...); },
+                    pkpy::BindType::DEFAULT,
+                    extra...);
+                return *this;
+            }
+        }
+
+        /// bind member function
+        template <typename Fn, typename... Extra>
+        class_& def(const char* name, Fn&& f, const Extra&... extra) {
+            using first = std::tuple_element_t<0, callable_args_t<remove_cvref_t<Fn>>>;
+            constexpr bool is_first_base_of_v =
+                std::is_reference_v<first> && std::is_base_of_v<T, remove_cvref_t<first>>;
+
+            if constexpr(!is_first_base_of_v) {
+                static_assert(
+                    is_first_base_of_v,
+                    "If you want to bind member function, the first argument must be the base class");
+            } else {
+                bind_function(*this, name, std::forward<Fn>(f), pkpy::BindType::DEFAULT, extra...);
+            }
+
+            return *this;
+        }
+
+        /// bind operators
+        template <typename Operator, typename... Extras>
+        class_& def(Operator op, const Extras&... extras) {
+            op.execute(*this, extras...);
+            return *this;
+        }
+
+        // TODO: factory function
+
+        /// bind static function
+        template <typename Fn, typename... Extra>
+        class_& def_static(const char* name, Fn&& f, const Extra&... extra) {
+            bind_function(*this, name, std::forward<Fn>(f), pkpy::BindType::STATICMETHOD, extra...);
+            return *this;
+        }
+
+        template <typename MP, typename... Extras>
+        class_& def_readwrite(const char* name, MP mp, const Extras&... extras) {
+            if constexpr(!std::is_member_object_pointer_v<MP>) {
+                static_assert(std::is_member_object_pointer_v<MP>,
+                              "def_readwrite only supports pointer to data member");
+            } else {
+                bind_property(*this, name, mp, mp, extras...);
+            }
+            return *this;
+        }
+
+        template <typename MP, typename... Extras>
+        class_& def_readonly(const char* name, MP mp, const Extras&... extras) {
+            if constexpr(!std::is_member_object_pointer_v<MP>) {
+                static_assert(std::is_member_object_pointer_v<MP>,
+                              "def_readonly only supports pointer to data member");
+            } else {
+                bind_property(*this, name, mp, nullptr, extras...);
+            }
+            return *this;
+        }
+
+        template <typename Getter, typename Setter, typename... Extras>
+        class_& def_property(const char* name, Getter&& g, Setter&& s, const Extras&... extras) {
+            bind_property(*this, name, std::forward<Getter>(g), std::forward<Setter>(s), extras...);
+            return *this;
+        }
+
+        template <typename Getter, typename... Extras>
+        class_& def_property_readonly(const char* name, Getter&& mp, const Extras&... extras) {
+            bind_property(*this, name, std::forward<Getter>(mp), nullptr, extras...);
+            return *this;
+        }
+
+        template <typename Var, typename... Extras>
+        class_& def_readwrite_static(const char* name, Var& mp, const Extras&... extras) {
+            static_assert(
+                dependent_false<Var>,
+                "define static properties requires metaclass. This is a complex feature with few use cases, so it may never be implemented.");
+            return *this;
+        }
+
+        template <typename Var, typename... Extras>
+        class_& def_readonly_static(const char* name, Var& mp, const Extras&... extras) {
+            static_assert(
+                dependent_false<Var>,
+                "define static properties requires metaclass. This is a complex feature with few use cases, so it may never be implemented.");
+            return *this;
+        }
+
+        template <typename Getter, typename Setter, typename... Extras>
+        class_&
+            def_property_static(const char* name, Getter&& g, Setter&& s, const Extras&... extras) {
+            static_assert(
+                dependent_false<Getter>,
+                "define static properties requires metaclass. This is a complex feature with few use cases, so it may never be implemented.");
+            return *this;
+        }
+    };
+
+    template <typename T, typename... Others>
+    class enum_ : public class_<T, Others...> {
+        std::map<const char*, pkpy::PyVar> m_values;
+
+    public:
+        using class_<T, Others...>::class_;
+
+        template <typename... Args>
+        enum_(const handle& scope, const char* name, Args&&... args) :
+            class_<T, Others...>(scope, name, std::forward<Args>(args)...) {}
+
+        enum_& value(const char* name, T value) {
+            handle var = type_caster<T>::cast(value, return_value_policy::copy);
+            this->m_ptr->attr().set(name, var.ptr());
+            m_values[name] = var.ptr();
+            return *this;
+        }
+
+        enum_& export_values() {
+            pkpy::PyVar mod = this->m_ptr->attr("__module__");
+            for(auto& [name, value]: m_values) {
+                mod->attr().set(name, value);
+            }
+            return *this;
+        }
+    };
+}  // namespace pybind11
diff --git a/include/pybind11/internal/cpp_function.h b/include/pybind11/internal/cpp_function.h
new file mode 100644
index 00000000..2f073c42
--- /dev/null
+++ b/include/pybind11/internal/cpp_function.h
@@ -0,0 +1,383 @@
+#pragma once
+
+#include "cast.h"
+#include <bitset>
+
+namespace pybind11 {
+
+    template <std::size_t Nurse, std::size_t... Patients>
+    struct keep_alive {};
+
+    template <typename T>
+    struct call_guard {
+        static_assert(std::is_default_constructible_v<T>,
+                      "call_guard must be default constructible");
+    };
+
+    // append the overload to the beginning of the overload list
+    struct prepend {};
+
+    template <typename... Args>
+    struct init {};
+
+    // TODO: support more customized tags
+    // struct kw_only {};
+    //
+    // struct pos_only {};
+    //
+    // struct default_arg {};
+    //
+    // struct arg {
+    //    const char* name;
+    //    const char* description;
+    // };
+    //
+    // struct default_arg {
+    //    const char* name;
+    //    const char* description;
+    //    const char* value;
+    // };
+
+    template <typename Fn,
+              typename Extra,
+              typename Args = callable_args_t<std::decay_t<Fn>>,
+              typename IndexSequence = std::make_index_sequence<std::tuple_size_v<Args>>>
+    struct generator;
+
+    class function_record {
+        union {
+            void* data;
+            char buffer[16];
+        };
+
+        // TODO: optimize the function_record size to reduce memory usage
+        const char* name;
+        function_record* next;
+        void (*destructor)(function_record*);
+        return_value_policy policy = return_value_policy::automatic;
+        handle (*wrapper)(function_record&, pkpy::ArgsView, bool convert, handle parent);
+
+        template <typename Fn, typename Extra, typename Args, typename IndexSequence>
+        friend struct generator;
+
+    public:
+        template <typename Fn, typename... Extras>
+        function_record(Fn&& f, const char* name, const Extras&... extras) :
+            name(name), next(nullptr) {
+
+            if constexpr(sizeof(f) <= sizeof(buffer)) {
+                new (buffer) auto(std::forward<Fn>(f));
+                destructor = [](function_record* self) {
+                    reinterpret_cast<Fn*>(self->buffer)->~Fn();
+                };
+            } else {
+                data = new auto(std::forward<Fn>(f));
+                destructor = [](function_record* self) { delete static_cast<Fn*>(self->data); };
+            }
+
+            using Generator = generator<std::decay_t<Fn>, std::tuple<Extras...>>;
+            Generator::initialize(*this, extras...);
+            wrapper = Generator::generate();
+        }
+
+        ~function_record() { destructor(this); }
+
+        template <typename Fn>
+        auto& cast() {
+            if constexpr(sizeof(Fn) <= sizeof(buffer)) {
+                return *reinterpret_cast<Fn*>(buffer);
+            } else {
+                return *static_cast<Fn*>(data);
+            }
+        }
+
+        void append(function_record* record) {
+            function_record* p = this;
+            while(p->next != nullptr) {
+                p = p->next;
+            }
+            p->next = record;
+        }
+
+        handle operator() (pkpy::ArgsView view) {
+            function_record* p = this;
+            // foreach function record and call the function with not convert
+            while(p != nullptr) {
+                handle result = p->wrapper(*this, view, false, {});
+                if(result) {
+                    return result;
+                }
+                p = p->next;
+            }
+
+            p = this;
+            // foreach function record and call the function with convert
+            while(p != nullptr) {
+                handle result = p->wrapper(*this, view, true, {});
+                if(result) {
+                    return result;
+                }
+                p = p->next;
+            }
+
+            vm->TypeError("no matching function found");
+        }
+    };
+
+    template <typename Fn, std::size_t... Is, typename... Args>
+    handle invoke(Fn&& fn,
+                  std::index_sequence<Is...>,
+                  std::tuple<type_caster<Args>...>& casters,
+                  return_value_policy policy,
+                  handle parent) {
+        using underlying_type = std::decay_t<Fn>;
+        using ret = callable_return_t<underlying_type>;
+
+        // if the return type is void, return None
+        if constexpr(std::is_void_v<ret>) {
+            // resolve the member function pointer
+            if constexpr(std::is_member_function_pointer_v<underlying_type>) {
+                [&](class_type_t<underlying_type>& self, auto&... args) {
+                    (self.*fn)(args...);
+                }(std::get<Is>(casters).value...);
+            } else {
+                fn(std::get<Is>(casters).value...);
+            }
+            return vm->None;
+        } else {
+            // resolve the member function pointer
+            if constexpr(std::is_member_function_pointer_v<remove_cvref_t<Fn>>) {
+                return type_caster<ret>::cast(
+                    [&](class_type_t<underlying_type>& self, auto&... args) {
+                        return (self.*fn)(args...);
+                    }(std::get<Is>(casters).value...),
+                    policy,
+                    parent);
+            } else {
+                return type_caster<ret>::cast(fn(std::get<Is>(casters).value...), policy, parent);
+            }
+        }
+    }
+
+    template <typename Fn, typename... Args, std::size_t... Is, typename... Extras>
+    struct generator<Fn, std::tuple<Extras...>, std::tuple<Args...>, std::index_sequence<Is...>> {
+        static void initialize(function_record& record, const Extras&... extras) {}
+
+        static auto generate() {
+            return +[](function_record& self, pkpy::ArgsView view, bool convert, handle parent) {
+                // FIXME:
+                // Temporarily, args and kwargs must be at the end of the arguments list
+                // Named arguments are not supported yet
+                constexpr bool has_args = types_count_v<args, remove_cvref_t<Args>...> != 0;
+                constexpr bool has_kwargs = types_count_v<kwargs, remove_cvref_t<Args>...> != 0;
+                constexpr std::size_t count = sizeof...(Args) - has_args - has_kwargs;
+
+                handle stack[sizeof...(Args)] = {};
+
+                // initialize the stack
+
+                if(!has_args && (view.size() != count)) {
+                    return handle();
+                }
+
+                if(has_args && (view.size() < count)) {
+                    return handle();
+                }
+
+                for(std::size_t i = 0; i < count; ++i) {
+                    stack[i] = view[i];
+                }
+
+                // pack the args and kwargs
+                if constexpr(has_args) {
+                    const auto n = view.size() - count;
+                    pkpy::PyVar var = vm->new_object<pkpy::Tuple>(vm->tp_tuple, n);
+                    auto& tuple = var.obj_get<pkpy::Tuple>();
+                    for(std::size_t i = 0; i < n; ++i) {
+                        tuple[i] = view[count + i];
+                    }
+                    stack[count] = var;
+                }
+
+                if constexpr(has_kwargs) {
+                    const auto n = vm->s_data._sp - view.end();
+                    pkpy::PyVar var = vm->new_object<pkpy::Dict>(vm->tp_dict);
+                    auto& dict = var.obj_get<pkpy::Dict>();
+
+                    for(std::size_t i = 0; i < n; i += 2) {
+                        pkpy::i64 index = pkpy::_py_cast<pkpy::i64>(vm, view[count + i]);
+                        pkpy::PyVar str =
+                            vm->new_object<pkpy::Str>(vm->tp_str, pkpy::StrName(index).sv());
+                        dict.set(vm, str, view[count + i + 1]);
+                    }
+
+                    stack[count + 1] = var;
+                }
+
+                // check if all the arguments are not valid
+                for(std::size_t i = 0; i < sizeof...(Args); ++i) {
+                    if(!stack[i]) {
+                        return handle();
+                    }
+                }
+
+                // ok, all the arguments are valid, call the function
+                std::tuple<type_caster<Args>...> casters;
+
+                // check type compatibility
+                if(((std::get<Is>(casters).load(stack[Is], convert)) && ...)) {
+                    return invoke(self.cast<Fn>(),
+                                  std::index_sequence<Is...>{},
+                                  casters,
+                                  self.policy,
+                                  parent);
+                }
+
+                return handle();
+            };
+        }
+    };
+
+    constexpr inline static auto _wrapper = +[](pkpy::VM*, pkpy::ArgsView view) {
+        auto& record = pkpy::lambda_get_userdata<function_record>(view.begin());
+        return record(view).ptr();
+    };
+
+    class cpp_function : public function {
+    public:
+        template <typename Fn, typename... Extras>
+        cpp_function(Fn&& f, const Extras&... extras) {
+            pkpy::any userdata = function_record(std::forward<Fn>(f), "anonymous", extras...);
+            m_ptr = vm->bind_func(nullptr, "", -1, _wrapper, std::move(userdata));
+            inc_ref();
+        }
+    };
+
+    template <typename Fn, typename... Extras>
+    handle bind_function(const handle& obj,
+                         const char* name,
+                         Fn&& fn,
+                         pkpy::BindType type,
+                         const Extras&... extras) {
+        // do not use cpp_function directly to avoid unnecessary reference count change
+        pkpy::PyVar var = obj.ptr();
+        pkpy::PyVar callable = var->attr().try_get(name);
+
+        // if the function is not bound yet, bind it
+        if(!callable) {
+            pkpy::any userdata = function_record(std::forward<Fn>(fn), name, extras...);
+            callable = vm->bind_func(var, name, -1, _wrapper, std::move(userdata));
+        } else {
+            auto& userdata = callable.obj_get<pkpy::NativeFunc>()._userdata;
+            function_record* record = new function_record(std::forward<Fn>(fn), name, extras...);
+
+            constexpr bool is_prepend = (types_count_v<prepend, Extras...> != 0);
+            if constexpr(is_prepend) {
+                // if prepend is specified, append the new record to the beginning of the list
+                function_record* last = (function_record*)userdata.data;
+                userdata.data = record;
+                record->append(last);
+            } else {
+                // otherwise, append the new record to the end of the list
+                function_record* last = (function_record*)userdata.data;
+                last->append(record);
+            }
+        }
+        return callable;
+    }
+
+    template <typename Getter_, typename Setter_, typename... Extras>
+    handle bind_property(const handle& obj,
+                         const char* name,
+                         Getter_&& getter_,
+                         Setter_&& setter_,
+                         const Extras&... extras) {
+        pkpy::PyVar var = obj.ptr();
+        pkpy::PyVar getter = vm->None;
+        pkpy::PyVar setter = vm->None;
+        using Getter = std::decay_t<Getter_>;
+        using Setter = std::decay_t<Setter_>;
+
+        getter = vm->new_object<pkpy::NativeFunc>(
+            vm->tp_native_func,
+            [](pkpy::VM* vm, pkpy::ArgsView view) -> pkpy::PyVar {
+                auto& getter = pkpy::lambda_get_userdata<Getter>(view.begin());
+
+                if constexpr(std::is_member_pointer_v<Getter>) {
+                    using Self = class_type_t<Getter>;
+                    auto& self = _builtin_cast<instance>(view[0]).cast<Self>();
+
+                    if constexpr(std::is_member_object_pointer_v<Getter>) {
+                        return type_caster<member_type_t<Getter>>::cast(
+                                   self.*getter,
+                                   return_value_policy::reference_internal,
+                                   view[0])
+                            .ptr();
+                    } else {
+                        return type_caster<callable_return_t<Getter>>::cast(
+                                   (self.*getter)(),
+                                   return_value_policy::reference_internal,
+                                   view[0])
+                            .ptr();
+                    }
+
+                } else {
+                    using Self = std::tuple_element_t<0, callable_args_t<Getter>>;
+                    auto& self = _builtin_cast<instance>(view[0]).cast<Self>();
+
+                    return type_caster<callable_return_t<Getter>>::cast(
+                               getter(self),
+                               return_value_policy::reference_internal,
+                               view[0])
+                        .ptr();
+                }
+            },
+            1,
+            std::forward<Getter_>(getter_));
+
+        if constexpr(!std::is_same_v<Setter, std::nullptr_t>) {
+            setter = vm->new_object<pkpy::NativeFunc>(
+                vm->tp_native_func,
+                [](pkpy::VM* vm, pkpy::ArgsView view) -> pkpy::PyVar {
+                    auto& setter = pkpy::lambda_get_userdata<Setter>(view.begin());
+
+                    if constexpr(std::is_member_pointer_v<Setter>) {
+                        using Self = class_type_t<Setter>;
+                        auto& self = _builtin_cast<instance>(view[0]).cast<Self>();
+
+                        if constexpr(std::is_member_object_pointer_v<Setter>) {
+                            type_caster<member_type_t<Setter>> caster;
+                            if(caster.load(view[1], true)) {
+                                self.*setter = caster.value;
+                                return vm->None;
+                            }
+                        } else {
+                            type_caster<std::tuple_element_t<1, callable_args_t<Setter>>> caster;
+                            if(caster.load(view[1], true)) {
+                                (self.*setter)(caster.value);
+                                return vm->None;
+                            }
+                        }
+                    } else {
+                        using Self = std::tuple_element_t<0, callable_args_t<Setter>>;
+                        auto& self = _builtin_cast<instance>(view[0]).cast<Self>();
+
+                        type_caster<std::tuple_element_t<1, callable_args_t<Setter>>> caster;
+                        if(caster.load(view[1], true)) {
+                            setter(self, caster.value);
+                            return vm->None;
+                        }
+                    }
+
+                    vm->TypeError("invalid argument");
+                },
+                2,
+                std::forward<Setter_>(setter_));
+        }
+
+        pkpy::PyVar property = vm->new_object<pkpy::Property>(vm->tp_property, getter, setter);
+        var->attr().set(name, property);
+        return property;
+    }
+
+}  // namespace pybind11
diff --git a/include/pybind11/internal/instance.h b/include/pybind11/internal/instance.h
new file mode 100644
index 00000000..dae3baec
--- /dev/null
+++ b/include/pybind11/internal/instance.h
@@ -0,0 +1,147 @@
+#pragma once
+
+#include "kernel.h"
+
+namespace pybind11 {
+    struct type_info {
+        const char* name;
+        std::size_t size;
+        std::size_t alignment;
+        void (*destructor)(void*);
+        void (*copy)(void*, const void*);
+        void (*move)(void*, void*);
+        const std::type_info* type;
+
+        template <typename T>
+        static type_info& of() {
+            static_assert(!std::is_reference_v<T> && !std::is_const_v<std::remove_reference_t<T>>,
+                          "T must not be a reference type or const type.");
+            static type_info info = {
+                typeid(T).name(),
+                sizeof(T),
+                alignof(T),
+                [](void* ptr) {
+                    ((T*)ptr)->~T();
+                    operator delete (ptr);
+                },
+                [](void* dst, const void* src) { new (dst) T(*(const T*)src); },
+                [](void* dst, void* src) { new (dst) T(std::move(*(T*)src)); },
+                &typeid(T),
+            };
+            return info;
+        }
+    };
+
+    // all registered C++ class will be ensured as instance type.
+    class instance {
+    public:
+        // use to record the type information of C++ class.
+
+    private:
+        enum Flag {
+            None = 0,
+            Own = 1 << 0,  // if the instance is owned by C++ side.
+            Ref = 1 << 1,  // need to mark the parent object.
+        };
+
+        Flag flag;
+        void* data;
+        const type_info* type;
+        pkpy::PyVar parent;
+        // pkpy::PyVar
+
+    public:
+        instance() noexcept : flag(Flag::None), data(nullptr), type(nullptr), parent(nullptr) {}
+
+        instance(const instance&) = delete;
+
+        instance(instance&& other) noexcept :
+            flag(other.flag), data(other.data), type(other.type), parent(other.parent) {
+            other.flag = Flag::None;
+            other.data = nullptr;
+            other.type = nullptr;
+            other.parent = nullptr;
+        }
+
+        template <typename T>
+        static pkpy::PyVar create(pkpy::Type type) {
+            instance instance;
+            instance.type = &type_info::of<T>();
+            instance.data = operator new (sizeof(T));
+            instance.flag = Flag::Own;
+            return vm->new_object<pybind11::instance>(type, std::move(instance));
+        }
+
+        template <typename T>
+        static pkpy::PyVar
+            create(T&& value,
+                   pkpy::Type type,
+                   return_value_policy policy = return_value_policy::automatic_reference,
+                   pkpy::PyVar parent = nullptr) noexcept {
+            using underlying_type = std::remove_cv_t<std::remove_reference_t<T>>;
+
+            // resolve for automatic policy.
+            if(policy == return_value_policy::automatic) {
+                policy = std::is_pointer_v<underlying_type> ? return_value_policy::take_ownership
+                         : std::is_lvalue_reference_v<T&&>  ? return_value_policy::copy
+                                                            : return_value_policy::move;
+            } else if(policy == return_value_policy::automatic_reference) {
+                policy = std::is_pointer_v<underlying_type> ? return_value_policy::reference
+                         : std::is_lvalue_reference_v<T&&>  ? return_value_policy::copy
+                                                            : return_value_policy::move;
+            }
+
+            auto& _value = [&]() -> auto& {
+                /**
+                 * note that, pybind11 will ignore the const qualifier.
+                 * in fact, try to modify a const value will result in undefined behavior.
+                 */
+                if constexpr(std::is_pointer_v<underlying_type>) {
+                    return *reinterpret_cast<underlying_type*>(value);
+                } else {
+                    return const_cast<underlying_type&>(value);
+                }
+            }();
+
+            instance instance;
+            instance.type = &type_info::of<underlying_type>();
+
+            if(policy == return_value_policy::take_ownership) {
+                instance.data = &_value;
+                instance.flag = Flag::Own;
+            } else if(policy == return_value_policy::copy) {
+                instance.data = ::new auto(_value);
+                instance.flag = Flag::Own;
+            } else if(policy == return_value_policy::move) {
+                instance.data = ::new auto(std::move(_value));
+                instance.flag = Flag::Own;
+            } else if(policy == return_value_policy::reference) {
+                instance.data = &_value;
+                instance.flag = Flag::None;
+            } else if(policy == return_value_policy::reference_internal) {
+                instance.data = &_value;
+                instance.flag = Flag::Ref;
+                instance.parent = parent;
+            }
+
+            return vm->new_object<pybind11::instance>(type, std::move(instance));
+        }
+
+        ~instance() {
+            if(flag & Flag::Own) {
+                type->destructor(data);
+            }
+        }
+
+        void _gc_mark(pkpy::VM* vm) const noexcept {
+            if(parent && (flag & Flag::Ref)) {
+                PK_OBJ_MARK(parent);
+            }
+        }
+
+        template <typename T>
+        T& cast() noexcept {
+            return *static_cast<T*>(data);
+        }
+    };
+}  // namespace pybind11
diff --git a/include/pybind11/internal/kernel.h b/include/pybind11/internal/kernel.h
new file mode 100644
index 00000000..b84fc9c3
--- /dev/null
+++ b/include/pybind11/internal/kernel.h
@@ -0,0 +1,108 @@
+#pragma once
+
+#include <pocketpy.h>
+
+namespace pybind11
+{
+    inline pkpy::VM* vm = nullptr;
+    inline std::map<pkpy::PyVar, int*>* _ref_counts_map = nullptr;
+
+    inline void initialize(bool enable_os = true)
+    {
+        vm = new pkpy::VM(enable_os);
+        _ref_counts_map = new std::map<pkpy::PyVar, int*>();
+
+        // use to keep alive PyObject, when the object is hold by C++ side.
+        vm->heap._gc_marker_ex = [](pkpy::VM* vm)
+        {
+            for(auto iter = _ref_counts_map->begin(); iter != _ref_counts_map->end();)
+            {
+                auto ref_count = iter->second;
+                if(*ref_count != 0)
+                {
+                    // if ref count is not zero, then mark it.
+                    PK_OBJ_MARK(iter->first);
+                    ++iter;
+                }
+                else
+                {
+                    // if ref count is zero, then delete it.
+                    iter = _ref_counts_map->erase(iter);
+                    delete ref_count;
+                }
+            }
+        };
+    }
+
+    inline void finalize()
+    {
+        delete _ref_counts_map;
+        delete vm;
+    }
+
+    enum class return_value_policy : uint8_t
+    {
+        /**
+         *  This is the default return value policy, which falls back to the policy
+         *  return_value_policy::take_ownership when the return value is a pointer.
+         *  Otherwise, it uses return_value::move or return_value::copy for rvalue
+         *  and lvalue references, respectively. See below for a description of what
+         *  all of these different policies do.
+         */
+        automatic = 0,
+
+        /**
+         *  As above, but use policy return_value_policy::reference when the return
+         *  value is a pointer. This is the default conversion policy for function
+         *  arguments when calling Python functions manually from C++ code (i.e. via
+         *  handle::operator()). You probably won't need to use this.
+         */
+        automatic_reference,
+
+        /**
+         *  Reference an existing object (i.e. do not create a new copy) and take
+         *  ownership. Python will call the destructor and delete operator when the
+         *  object's reference count reaches zero. Undefined behavior ensues when
+         *  the C++ side does the same..
+         */
+        take_ownership,
+
+        /**
+         *  Create a new copy of the returned object, which will be owned by
+         *  Python. This policy is comparably safe because the lifetimes of the two
+         *  instances are decoupled.
+         */
+        copy,
+
+        /**
+         *  Use std::move to move the return value contents into a new instance
+         *  that will be owned by Python. This policy is comparably safe because the
+         *  lifetimes of the two instances (move source and destination) are
+         *  decoupled.
+         */
+        move,
+
+        /**
+         *  Reference an existing object, but do not take ownership. The C++ side
+         *  is responsible for managing the object's lifetime and deallocating it
+         *  when it is no longer used. Warning: undefined behavior will ensue when
+         *  the C++ side deletes an object that is still referenced and used by
+         *  Python.
+         */
+        reference,
+
+        /**
+         *  This policy only applies to methods and properties. It references the
+         *  object without taking ownership similar to the above
+         *  return_value_policy::reference policy. In contrast to that policy, the
+         *  function or property's implicit this argument (called the parent) is
+         *  considered to be the the owner of the return value (the child).
+         *  pybind11 then couples the lifetime of the parent to the child via a
+         *  reference relationship that ensures that the parent cannot be garbage
+         *  collected while Python is still using the child. More advanced
+         *  variations of this scheme are also possible using combinations of
+         *  return_value_policy::reference and the keep_alive call policy
+         */
+        reference_internal
+    };
+}  // namespace pybind11
diff --git a/include/pybind11/internal/object.h b/include/pybind11/internal/object.h
new file mode 100644
index 00000000..ab9b7f0a
--- /dev/null
+++ b/include/pybind11/internal/object.h
@@ -0,0 +1,256 @@
+#pragma once
+
+#include "kernel.h"
+
+namespace pybind11 {
+    class handle;
+    class object;
+    class attr_accessor;
+    class item_accessor;
+    class iterator;
+    class str;
+    class bytes;
+    class iterable;
+    class tuple;
+    class dict;
+    class list;
+    class set;
+    class function;
+    class module;
+    class type;
+    class bool_;
+    class int_;
+    class float_;
+    class str;
+    class bytes;
+
+    template <typename T>
+    T& _builtin_cast(const handle& obj);
+
+    template <typename T>
+    T reinterpret_borrow(const handle& h);
+
+    template <typename T>
+    T reinterpret_steal(const handle& h);
+
+    class handle {
+    protected:
+        pkpy::PyVar m_ptr = nullptr;
+        mutable int* ref_count = nullptr;
+
+    public:
+        handle() = default;
+        handle(const handle& h) = default;
+        handle& operator= (const handle& other) = default;
+
+        handle(pkpy::PyVar ptr) : m_ptr(ptr) {}
+
+        pkpy::PyVar ptr() const { return m_ptr; }
+
+        int reference_count() const { return ref_count == nullptr ? 0 : *ref_count; }
+
+        const handle& inc_ref() const {
+            PK_DEBUG_ASSERT(m_ptr != nullptr);
+            if(ref_count == nullptr) {
+                auto iter = _ref_counts_map->find(m_ptr);
+                if(iter == _ref_counts_map->end()) {
+                    ref_count = ::new int(1);
+                    _ref_counts_map->insert({m_ptr, ref_count});
+                } else {
+                    ref_count = iter->second;
+                    *ref_count += 1;
+                }
+            } else {
+                *ref_count += 1;
+            }
+            return *this;
+        }
+
+        const handle& dec_ref() const {
+            PK_DEBUG_ASSERT(m_ptr != nullptr);
+            PK_DEBUG_ASSERT(ref_count != nullptr);
+
+            *ref_count -= 1;
+            try {
+                if(*ref_count == 0) {
+                    _ref_counts_map->erase(m_ptr);
+                    ::delete ref_count;
+                    ref_count = nullptr;
+                }
+            } catch(std::exception& e) { std::cerr << "Error: " << e.what() << std::endl; }
+
+            return *this;
+        }
+
+    public:
+        template <typename T>
+        T cast() const;
+
+        explicit operator bool () const { return m_ptr.operator bool (); }
+
+        bool is(const handle& other) const { return m_ptr == other.m_ptr; }
+
+        bool is_none() const { return m_ptr == vm->None; }
+
+        bool in(const handle& other) const {
+            return pkpy::py_cast<bool>(vm, vm->call(vm->py_op("contains"), other.m_ptr, m_ptr));
+        }
+
+        bool contains(const handle& other) const {
+            return pkpy::py_cast<bool>(vm, vm->call(vm->py_op("contains"), m_ptr, other.m_ptr));
+        }
+
+        iterator begin() const;
+        iterator end() const;
+
+        str doc() const;
+
+        attr_accessor attr(const char* name) const;
+        attr_accessor attr(const handle& name) const;
+        attr_accessor attr(object&& name) const;
+
+        item_accessor operator[] (int64_t key) const;
+        item_accessor operator[] (const char* key) const;
+        item_accessor operator[] (const handle& key) const;
+        item_accessor operator[] (object&& key) const;
+
+        object operator- () const;
+        object operator~() const;
+
+        template <return_value_policy policy = return_value_policy::automatic, typename... Args>
+        object operator() (Args&&... args) const;
+
+    private:
+        friend object operator+ (const handle& lhs, const handle& rhs);
+        friend object operator- (const handle& lhs, const handle& rhs);
+        friend object operator* (const handle& lhs, const handle& rhs);
+        friend object operator% (const handle& lhs, const handle& rhs);
+        friend object operator/ (const handle& lhs, const handle& rhs);
+        friend object operator| (const handle& lhs, const handle& rhs);
+        friend object operator& (const handle& lhs, const handle& rhs);
+        friend object operator^ (const handle& lhs, const handle& rhs);
+        friend object operator<< (const handle& lhs, const handle& rhs);
+        friend object operator>> (const handle& lhs, const handle& rhs);
+
+        friend object operator+= (const handle& lhs, const handle& rhs);
+        friend object operator-= (const handle& lhs, const handle& rhs);
+        friend object operator*= (const handle& lhs, const handle& rhs);
+        friend object operator/= (const handle& lhs, const handle& rhs);
+        friend object operator%= (const handle& lhs, const handle& rhs);
+        friend object operator|= (const handle& lhs, const handle& rhs);
+        friend object operator&= (const handle& lhs, const handle& rhs);
+        friend object operator^= (const handle& lhs, const handle& rhs);
+        friend object operator<<= (const handle& lhs, const handle& rhs);
+        friend object operator>>= (const handle& lhs, const handle& rhs);
+
+        friend object operator== (const handle& lhs, const handle& rhs);
+        friend object operator!= (const handle& lhs, const handle& rhs);
+        friend object operator< (const handle& lhs, const handle& rhs);
+        friend object operator> (const handle& lhs, const handle& rhs);
+        friend object operator<= (const handle& lhs, const handle& rhs);
+        friend object operator>= (const handle& lhs, const handle& rhs);
+
+        template <typename T>
+        friend T& _builtin_cast(const handle& obj) {
+            // FIXME: 2.0 does not use Py_<T> anymore
+            static_assert(!std::is_reference_v<T>, "T must not be a reference type.");
+            return obj.ptr().obj_get<T>();
+        }
+    };
+
+    static_assert(std::is_trivially_copyable_v<handle>);
+
+    class object : public handle {
+    public:
+        object(const object& other) : handle(other) { inc_ref(); }
+
+        object(object&& other) noexcept : handle(other) {
+            other.m_ptr = nullptr;
+            other.ref_count = nullptr;
+        }
+
+        object& operator= (const object& other) {
+            if(this != &other) {
+                dec_ref();
+                m_ptr = other.m_ptr;
+                ref_count = other.ref_count;
+                inc_ref();
+            }
+            return *this;
+        }
+
+        object& operator= (object&& other) noexcept {
+            if(this != &other) {
+                dec_ref();
+                m_ptr = other.m_ptr;
+                ref_count = other.ref_count;
+                other.m_ptr = nullptr;
+                other.ref_count = nullptr;
+            }
+            return *this;
+        }
+
+        ~object() {
+            if(m_ptr != nullptr) {
+                dec_ref();
+            }
+        }
+
+    protected:
+        object(const handle& h, bool borrow) : handle(h) {
+            if(borrow) {
+                inc_ref();
+            }
+        }
+
+        template <typename T>
+        friend T reinterpret_borrow(const handle& h) {
+            return {h, true};
+        }
+
+        template <typename T>
+        friend T reinterpret_steal(const handle& h) {
+            return {h, false};
+        }
+    };
+
+    inline void setattr(const handle& obj, const handle& name, const handle& value);
+    inline void setitem(const handle& obj, const handle& key, const handle& value);
+
+#define PYBIND11_BINARY_OPERATOR(OP, NAME)                                                         \
+    inline object operator OP (const handle& lhs, const handle& rhs) {                             \
+        return reinterpret_borrow<object>(vm->call(vm->py_op(NAME), lhs.m_ptr, rhs.m_ptr));        \
+    }
+
+    PYBIND11_BINARY_OPERATOR(+, "add");
+    PYBIND11_BINARY_OPERATOR(-, "sub");
+    PYBIND11_BINARY_OPERATOR(*, "mul");
+    PYBIND11_BINARY_OPERATOR(/, "truediv");
+    PYBIND11_BINARY_OPERATOR(%, "mod");
+    PYBIND11_BINARY_OPERATOR(|, "or_");
+    PYBIND11_BINARY_OPERATOR(&, "and_");
+    PYBIND11_BINARY_OPERATOR(^, "xor");
+    PYBIND11_BINARY_OPERATOR(<<, "lshift");
+    PYBIND11_BINARY_OPERATOR(>>, "rshift");
+
+    PYBIND11_BINARY_OPERATOR(+=, "iadd");
+    PYBIND11_BINARY_OPERATOR(-=, "isub");
+    PYBIND11_BINARY_OPERATOR(*=, "imul");
+    PYBIND11_BINARY_OPERATOR(/=, "itruediv");
+    PYBIND11_BINARY_OPERATOR(%=, "imod");
+    PYBIND11_BINARY_OPERATOR(|=, "ior");
+    PYBIND11_BINARY_OPERATOR(&=, "iand");
+    PYBIND11_BINARY_OPERATOR(^=, "ixor");
+    PYBIND11_BINARY_OPERATOR(<<=, "ilshift");
+    PYBIND11_BINARY_OPERATOR(>>=, "irshift");
+
+    PYBIND11_BINARY_OPERATOR(==, "eq");
+    PYBIND11_BINARY_OPERATOR(!=, "ne");
+    PYBIND11_BINARY_OPERATOR(<, "lt");
+    PYBIND11_BINARY_OPERATOR(>, "gt");
+    PYBIND11_BINARY_OPERATOR(<=, "le");
+    PYBIND11_BINARY_OPERATOR(>=, "ge");
+
+#undef PYBIND11_BINARY_OPERATOR
+
+}  // namespace pybind11
diff --git a/include/pybind11/internal/type_traits.h b/include/pybind11/internal/type_traits.h
new file mode 100644
index 00000000..124d539d
--- /dev/null
+++ b/include/pybind11/internal/type_traits.h
@@ -0,0 +1,157 @@
+#pragma once
+
+#include <tuple>
+#include <type_traits>
+
+namespace pybind11 {
+    template <typename T>
+    constexpr bool dependent_false = false;
+
+    template <typename T, typename Tuple>
+    struct tuple_push_front;
+
+    template <typename T, typename... Ts>
+    struct tuple_push_front<T, std::tuple<Ts...>> {
+        using type = std::tuple<T, Ts...>;
+    };
+
+    template <typename T, typename Tuple>
+    using tuple_push_front_t = typename tuple_push_front<T, Tuple>::type;
+
+    // traits for function types
+    template <typename Fn>
+    struct function_traits {
+        static_assert(dependent_false<Fn>, "unsupported function type");
+    };
+
+#define PYBIND11_FUNCTION_TRAITS_SPECIALIZE(qualifiers)                                            \
+    template <typename R, typename... Args>                                                        \
+    struct function_traits<R(Args...) qualifiers> {                                                \
+        using return_type = R;                                                                     \
+        using args_type = std::tuple<Args...>;                                                     \
+        constexpr static std::size_t args_count = sizeof...(Args);                                 \
+    };
+
+    PYBIND11_FUNCTION_TRAITS_SPECIALIZE()
+    PYBIND11_FUNCTION_TRAITS_SPECIALIZE(&)
+    PYBIND11_FUNCTION_TRAITS_SPECIALIZE(const)
+    PYBIND11_FUNCTION_TRAITS_SPECIALIZE(const&)
+    PYBIND11_FUNCTION_TRAITS_SPECIALIZE(noexcept)
+    PYBIND11_FUNCTION_TRAITS_SPECIALIZE(& noexcept)
+    PYBIND11_FUNCTION_TRAITS_SPECIALIZE(const noexcept)
+    PYBIND11_FUNCTION_TRAITS_SPECIALIZE(const& noexcept)
+
+#undef PYBIND11_FUNCTION_TRAITS_SPECIALIZE
+
+    template <typename T>
+    using function_return_t = typename function_traits<T>::return_type;
+
+    template <typename T>
+    using function_args_t = typename function_traits<T>::args_type;
+
+    template <typename T>
+    constexpr std::size_t function_args_count = function_traits<T>::args_count;
+
+    // traits for member pointers
+    template <typename T>
+    struct member_traits;
+
+    template <typename M, typename C>
+    struct member_traits<M C::*> {
+        using member_type = M;
+        using class_type = C;
+    };
+
+    template <typename T>
+    using member_type_t = typename member_traits<T>::member_type;
+
+    template <typename T>
+    using class_type_t = typename member_traits<T>::class_type;
+
+    // some traits for distinguishing between function pointers, member function pointers and
+    // functors
+    using std::is_member_function_pointer_v;
+    using std::is_member_object_pointer_v;
+
+    template <typename T>
+    constexpr inline bool is_function_pointer_v = std::is_function_v<std::remove_pointer_t<T>>;
+
+    template <typename T, typename U = void>
+    constexpr bool is_functor_v = false;
+
+    template <typename T>
+    constexpr inline bool is_functor_v<T, std::void_t<decltype(&T::operator())>> = true;
+
+    template <typename T, typename SFINAE = void>
+    struct callable_traits;
+
+    template <typename T>
+    struct callable_traits<T, std::enable_if_t<is_member_function_pointer_v<T>>> {
+        using args_type = tuple_push_front_t<class_type_t<T>&, function_args_t<member_type_t<T>>>;
+        using return_type = function_return_t<member_type_t<T>>;
+    };
+
+    template <typename T>
+    struct callable_traits<T, std::enable_if_t<is_function_pointer_v<T>>> {
+        using args_type = function_args_t<std::remove_pointer<T>>;
+        using return_type = function_return_t<std::remove_pointer<T>>;
+    };
+
+    template <typename T>
+    struct callable_traits<T, std::enable_if_t<is_functor_v<T>>> {
+        using args_type = function_args_t<member_type_t<decltype(&T::operator())>>;
+        using return_type = function_return_t<member_type_t<decltype(&T::operator())>>;
+    };
+
+    template <typename Callable>
+    using callable_args_t = typename callable_traits<Callable>::args_type;
+
+    template <typename Callable>
+    using callable_return_t = typename callable_traits<Callable>::return_type;
+
+    template <typename Callable>
+    constexpr std::size_t callable_args_count_v = std::tuple_size_v<callable_args_t<Callable>>;
+
+    template <typename T>
+    struct type_identity {
+        using type = T;
+    };
+
+    template <typename T>
+    using remove_cvref_t = std::remove_cv_t<std::remove_reference_t<T>>;
+
+    template <typename T, typename... Ts>
+    constexpr inline std::size_t types_count_v = (std::is_same_v<T, Ts> + ...);
+
+    template <typename T>
+    constexpr inline std::size_t types_count_v<T> = 0;
+
+    template <typename T>
+    struct value_wrapper {
+        T* pointer;
+
+        operator T& () { return *pointer; }
+    };
+
+    template <typename T>
+    struct value_wrapper<T*> {
+        T* pointer;
+
+        operator T* () { return pointer; }
+    };
+
+    template <typename T>
+    struct value_wrapper<T&> {
+        T* pointer;
+
+        operator T& () { return *pointer; }
+    };
+
+    template <typename T>
+    struct value_wrapper<T&&> {
+        T* pointer;
+
+        operator T&& () { return std::move(*pointer); }
+    };
+
+}  // namespace pybind11
diff --git a/include/pybind11/internal/types.h b/include/pybind11/internal/types.h
new file mode 100644
index 00000000..d223ad8f
--- /dev/null
+++ b/include/pybind11/internal/types.h
@@ -0,0 +1,218 @@
+#pragma once
+
+#include "object.h"
+
+namespace pybind11 {
+    class type : public object {
+    public:
+        using object::object;
+        template <typename T>
+        static handle handle_of();
+    };
+
+    class iterable : public object {
+    public:
+        using object::object;
+        iterable() = delete;
+    };
+
+    class iterator : public object {
+    public:
+        using object::object;
+        iterator() = delete;
+    };
+
+    class list : public object {
+    public:
+        using object::object;
+
+        list() : object(vm->new_object<pkpy::List>(pkpy::VM::tp_list), true) {}
+    };
+
+    class tuple : public object {
+    public:
+        using object::object;
+
+        tuple(int n) : object(vm->new_object<pkpy::Tuple>(pkpy::VM::tp_tuple, n), true) {}
+
+        //& operator[](int i){ return _args[i]; }
+        // PyVar operator[](int i) const { return _args[i]; }
+    };
+
+    class set : public object {
+    public:
+        using object::object;
+        // set() : object(vm->new_object<pkpy::Se>(pkpy::VM::tp_set), true) {}
+    };
+
+    class dict : public object {
+    public:
+        using object::object;
+
+        dict() : object(vm->new_object<pkpy::Dict>(pkpy::VM::tp_dict), true) {}
+    };
+
+    class str : public object {
+
+    public:
+        using object::object;
+        str(const char* c, int len) :
+            object(vm->new_object<pkpy::Str>(pkpy::VM::tp_str, c, len), true) {
+
+            };
+
+        str(const char* c = "") : str(c, strlen(c)) {}
+
+        str(const std::string& s) : str(s.data(), s.size()) {}
+
+        str(std::string_view sv) : str(sv.data(), sv.size()) {}
+
+        explicit str(const bytes& b);
+        explicit str(handle h);
+        operator std::string () const;
+
+        template <typename... Args>
+        str format(Args&&... args) const;
+    };
+
+    class int_ : public object {
+    public:
+        using object::object;
+
+        int_(int64_t value) : object(pkpy::py_var(vm, value), true) {}
+    };
+
+    class float_ : public object {
+    public:
+        using object::object;
+
+        float_(double value) : object(pkpy::py_var(vm, value), true) {}
+    };
+
+    class bool_ : public object {
+    public:
+        using object::object;
+
+        bool_(bool value) : object(pkpy::py_var(vm, value), true) {}
+    };
+
+    class function : public object {
+    public:
+        using object::object;
+    };
+
+    class attr_accessor : public object {
+    private:
+        object key;
+
+    public:
+        template <typename T>
+        attr_accessor(const object& obj, T&& key) : object(obj), key(std::forward<T>(key)){};
+
+        template <typename T>
+        attr_accessor& operator= (T&& value) & {
+            static_assert(std::is_base_of_v<object, std::decay_t<T>>,
+                          "T must be derived from object");
+            m_ptr = std::forward<T>(value);
+            return *this;
+        }
+
+        template <typename T>
+        attr_accessor& operator= (T&& value) && {
+            static_assert(std::is_base_of_v<object, std::decay_t<T>>,
+                          "T must be derived from object");
+            setattr(*this, key, std::forward<T>(value));
+            return *this;
+        }
+    };
+
+    inline attr_accessor handle::attr(const char* name) const {
+        return attr_accessor(reinterpret_borrow<object>(*this), str(name));
+    }
+
+    inline attr_accessor handle::attr(const handle& name) const {
+        return attr_accessor(reinterpret_borrow<object>(*this), reinterpret_borrow<object>(name));
+    }
+
+    inline attr_accessor handle::attr(object&& name) const {
+        return attr_accessor(reinterpret_borrow<object>(*this), std::move(name));
+    }
+
+    class item_accessor : public object {
+    public:
+        object key;
+
+    public:
+        template <typename T>
+        item_accessor(const object& obj, T&& key) : object(obj), key(std::forward<T>(key)){};
+
+        template <typename T>
+        item_accessor& operator= (T&& value) & {
+            static_assert(std::is_base_of_v<object, std::decay_t<T>>,
+                          "T must be derived from object");
+            m_ptr = std::forward<T>(value);
+        }
+
+        template <typename T>
+        item_accessor& operator= (object&& value) && {
+            static_assert(std::is_base_of_v<object, std::decay_t<T>>,
+                          "T must be derived from object");
+            setitem(*this, key, std::forward<T>(value));
+        }
+    };
+
+    inline item_accessor handle::operator[] (int64_t key) const {
+        return item_accessor(reinterpret_borrow<object>(*this), int_(key));
+    }
+
+    inline item_accessor handle::operator[] (const char* key) const {
+        return item_accessor(reinterpret_borrow<object>(*this), str(key));
+    }
+
+    inline item_accessor handle::operator[] (const handle& key) const {
+        return item_accessor(reinterpret_borrow<object>(*this), reinterpret_borrow<object>(key));
+    }
+
+    inline item_accessor handle::operator[] (object&& key) const {
+        return item_accessor(reinterpret_borrow<object>(*this), std::move(key));
+    }
+
+    class args : public tuple {
+        using tuple::tuple;
+    };
+
+    class kwargs : public dict {
+        using dict::dict;
+    };
+
+    template <typename T>
+    handle type::handle_of() {
+        if constexpr(std::is_same_v<T, object>) {
+            return vm->_t(vm->tp_object);
+        }
+#define PYBIND11_TYPE_MAPPER(type, tp)                                                             \
+    else if constexpr(std::is_same_v<T, type>) {                                                   \
+        return vm->_t(vm->tp);                                                                     \
+    }
+        PYBIND11_TYPE_MAPPER(type, tp_type)
+        PYBIND11_TYPE_MAPPER(str, tp_str)
+        PYBIND11_TYPE_MAPPER(int_, tp_int)
+        PYBIND11_TYPE_MAPPER(float_, tp_float)
+        PYBIND11_TYPE_MAPPER(bool_, tp_bool)
+        PYBIND11_TYPE_MAPPER(list, tp_list)
+        PYBIND11_TYPE_MAPPER(tuple, tp_tuple)
+        PYBIND11_TYPE_MAPPER(args, tp_tuple)
+        PYBIND11_TYPE_MAPPER(dict, tp_dict)
+        PYBIND11_TYPE_MAPPER(kwargs, tp_dict)
+#undef PYBIND11_TYPE_MAPPER
+        else {
+            auto result = vm->_cxx_typeid_map.find(typeid(T));
+            if(result != vm->_cxx_typeid_map.end()) {
+                return vm->_t(result->second);
+            }
+
+            vm->TypeError("Type not registered");
+        }
+    }
+
+}  // namespace pybind11
diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
new file mode 100644
index 00000000..3f35334d
--- /dev/null
+++ b/include/pybind11/pybind11.h
@@ -0,0 +1,3 @@
+#pragma once
+
+#include "internal/class.h"
\ No newline at end of file