commit 68dd99a8268c155012f331d2d3c38537bd82fb6a
Author: DarkSharpness <2040703891@qq.com>
Date:   Tue Jul 9 21:04:36 2024 +0800

    initial commit | complete a draft outline

diff --git a/demo/demo.cpp b/demo/demo.cpp
new file mode 100644
index 0000000..9060079
--- /dev/null
+++ b/demo/demo.cpp
@@ -0,0 +1,40 @@
+#include "../include/tools"
+
+struct Input {
+    Wire a;
+    Wire b;
+    std::array <Wire, 2> c;
+};
+
+struct Output {
+    Register d;
+    Register e;
+};
+
+struct Content {
+    Register r;
+};
+
+struct MyModule : Input, Output, private Content {
+    using Tags = SyncTags <Input, Output, Content>;
+    friend class Visitor;
+
+    void demo() {
+        this->d <= this->a + this->b;
+    }
+};
+
+signed main() {
+    MyModule m;
+
+    m.a = []() { return 1; };
+    m.b.assign([&]() { return (target_size_t)m.d; });
+
+    for (int i = 0 ; i < 10 ; ++i) {
+        std::cout << m.d << std::endl;
+        m.demo();
+        std::cout << m.d << std::endl;
+        sync_member(m);
+    }
+    return 0;
+}
diff --git a/include/debug.h b/include/debug.h
new file mode 100644
index 0000000..601d3f4
--- /dev/null
+++ b/include/debug.h
@@ -0,0 +1,61 @@
+#pragma once
+#include <utility>
+#include <iostream>
+#include <source_location>
+
+namespace dark::debug {
+
+/**
+ * Copied from https://en.cppreference.com/w/cpp/utility/unreachable 
+ * If compiled under C++23, just use std::unreachable() instead.
+*/
+[[noreturn]] inline void unreachable() {
+#if __cplusplus > 202002L
+    std::unreachable();
+#elif defined(_MSC_VER) && !defined(__clang__) // MSVC
+    // Uses compiler specific extensions if possible.
+    // Even if no extension is used, undefined behavior is still raised by
+    // an empty function body and the noreturn attribute.
+    __assume(false);
+#else // GCC, Clang
+    __builtin_unreachable();
+#endif
+}
+
+template <typename _Tp, typename... _Args>
+struct assert {
+    explicit assert(_Tp &&condition, _Args &&...args,
+        std::source_location location = std::source_location::current()) {
+        if (condition) return;
+        std::cerr << "Assertion failed at: "
+            << location.file_name() << ":" << location.line() << "\n";
+        if constexpr (sizeof...(args) != 0) {
+            std::cerr << "Message: ";
+            ((std::cerr << args), ...) << std::endl;
+        }
+        std::exit(EXIT_FAILURE);
+    }
+};
+
+template <typename _Tp, typename... _Args>
+assert(_Tp &&, _Args &&...) -> assert<_Tp, _Args...>;
+
+template <typename _Tp, _Tp _Default>
+struct DebugValue {
+#ifdef _DEBUG
+  private:
+    _Tp _M_value = _Default;
+  public:
+    auto get_value() const { return this->_M_value; }
+    auto set_value(_Tp value) { this->_M_value = value; }
+#else
+  public:
+    auto get_value() const { return _Default; }
+    auto set_value(_Tp) { /* do nothing */ }
+#endif
+  public:
+    explicit operator _Tp() const { return this->get_value(); }
+    DebugValue &operator=(_Tp value) { this->set_value(value); return *this; }
+};
+
+} // namespace dark::debug
diff --git a/include/hardware.h b/include/hardware.h
new file mode 100644
index 0000000..6f659ec
--- /dev/null
+++ b/include/hardware.h
@@ -0,0 +1,138 @@
+#pragma once
+#include "debug.h"
+#include "target.h"
+#include <memory>
+#include <concepts>
+
+namespace dark::hardware {
+
+struct Visitor;
+struct Wire;
+struct Register;
+
+template <typename _Fn>
+concept WireFunction =
+    !std::same_as <Wire, std::decay_t <_Fn>> &&
+    requires(_Fn &&__f) { { __f() } -> std::convertible_to <target_size_t>; };
+
+struct WireBase {
+    using _Ret_t = int;
+    using _Cpy_t = WireBase *;
+    virtual _Ret_t call() const = 0;
+    virtual ~WireBase() = default;
+};
+
+template <WireFunction _Fn>
+struct WireImpl final : WireBase {
+    _Fn _M_lambda;
+
+    template <typename _Fn2>
+    WireImpl(_Fn2 &&fn) : _M_lambda(std::forward <_Fn2>(fn)) {}
+
+    _Ret_t call() const override { return this->_M_lambda(); }
+};
+
+struct EmptyWire final : WireBase {
+    _Ret_t call() const override {
+        debug::assert(false, "Empty wire is called.");
+        debug::unreachable();
+    }
+};
+
+struct Wire {
+  private:
+    friend struct Visitor;
+
+    using _Manage_t = WireBase;
+
+    std::unique_ptr <_Manage_t>     _M_impl;
+    mutable target_size_t           _M_cache;
+    mutable bool                    _M_holds;
+
+    [[no_unique_address]]
+    debug::DebugValue <bool, false> _M_dirty; // Can be assigned only once
+
+    void sync() { this->_M_holds = false; }
+
+    template <WireFunction _Fn>
+    static auto _M_new_impl(_Fn &&fn) -> _Manage_t * {
+        return new WireImpl <std::decay_t<_Fn>> {std::forward <_Fn>(fn)};
+    }
+
+    void _M_check_double_assign() {
+        debug::assert(!this->_M_dirty, "Wire is already assigned.");
+        this->_M_dirty = true;
+    }
+
+  public:
+
+    Wire() : _M_impl(new EmptyWire), _M_cache(), _M_holds(), _M_dirty() {}
+
+    Wire(Wire &&) = delete;
+    Wire(const Wire &) = delete;
+    Wire &operator=(Wire &&) = delete;
+    Wire &operator=(const Wire &rhs) = delete;
+
+    template <WireFunction _Fn>
+    Wire(_Fn &&fn)
+        : _M_impl(_M_new_impl(std::forward <_Fn>(fn))), _M_cache(), _M_holds(), _M_dirty() {}
+
+    template <WireFunction _Fn>
+    Wire &operator=(_Fn &&fn) {
+        this->assign(std::forward <_Fn>(fn));
+        return *this;
+    }
+
+    template <WireFunction _Fn>
+    void assign(_Fn &&fn) {
+        this->_M_check_double_assign();
+        this->_M_impl.reset(this->_M_new_impl(std::forward <_Fn>(fn)));
+        this->_M_holds = false;
+    }
+
+    operator target_size_t() const {
+        if (this->_M_holds == false) {
+            this->_M_cache = this->_M_impl->call();
+            this->_M_holds = true;
+        }
+        return this->_M_cache;
+    }
+};
+
+struct Register {
+  private:
+    friend struct Visitor;
+
+    target_size_t _M_new;
+    target_size_t _M_old;
+
+    [[no_unique_address]]
+    debug::DebugValue <bool, false> _M_dirty;
+
+    void sync() {
+        if (this->_M_dirty) {
+            this->_M_old = this->_M_new;
+            this->_M_dirty = false;
+        }
+    }
+
+    void set_value(target_size_t value) {
+        this->_M_new = value;
+        debug::assert(!this->_M_dirty, "Register is already assigned in this cycle.");
+        this->_M_dirty = true;
+    }
+
+    auto get_value() const -> target_size_t { return this->_M_old; }
+
+  public:
+    Register() : _M_new(), _M_old(), _M_dirty() {}
+
+    template <std::convertible_to <target_size_t> _Int>
+    void operator <= (_Int &&value) {
+        this->set_value(static_cast <target_size_t>(value));
+    }
+
+    operator target_size_t() const { return this->get_value(); }
+};
+
+} // namespace dark::hardware
diff --git a/include/reflect.h b/include/reflect.h
new file mode 100644
index 0000000..d3a1dfd
--- /dev/null
+++ b/include/reflect.h
@@ -0,0 +1,81 @@
+#pragma once
+#include <tuple>
+#include <concepts>
+
+namespace dark::reflect {
+
+/* A init helper to get the size of a struct. */
+struct init_helper { template <typename _Tp> operator _Tp(); };
+
+/* A size helper to get the size of a struct. */
+template <typename _Tp> requires std::is_aggregate_v <_Tp>
+inline consteval auto member_size_aux(auto &&...args) -> std::size_t {
+    constexpr std::size_t size      = sizeof...(args);
+    constexpr std::size_t maximum   = 114;
+    if constexpr (size > maximum) {
+        static_assert (sizeof(_Tp) == 0, "The struct has too many members.");
+    } else if constexpr (!requires {_Tp { args... }; }) {
+        return size - 1;
+    } else {
+        return member_size_aux <_Tp> (args..., init_helper {});
+    }
+}
+
+/* Return the member size for a aggregate type without base.  */
+template <typename _Tp> requires std::is_aggregate_v <_Tp>
+inline consteval auto member_size(_Tp &) -> std::size_t { return member_size_aux <_Tp> (); }
+
+template <typename _Tp> requires std::is_aggregate_v <_Tp>
+inline consteval auto member_size() -> std::size_t { return member_size_aux <_Tp> (); }
+
+template <typename _Tp> requires std::is_aggregate_v <_Tp>
+auto tuplify(_Tp &value) {
+    constexpr auto size = member_size <_Tp> ();
+    if constexpr (size == 1) {
+        auto &[x0] = value;
+        return std::forward_as_tuple(x0);
+    } else if constexpr (size == 2) {
+        auto &[x0, x1] = value;
+        return std::forward_as_tuple(x0, x1);
+    } else if constexpr (size == 3) {
+        auto &[x0, x1, x2] = value;
+        return std::forward_as_tuple(x0, x1, x2);
+    } else if constexpr (size == 4) {
+        auto &[x0, x1, x2, x3] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3);
+    } else if constexpr (size == 5) {
+        auto &[x0, x1, x2, x3, x4] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4);
+    } else if constexpr (size == 6) {
+        auto &[x0, x1, x2, x3, x4, x5] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5);
+    } else if constexpr (size == 7) {
+        auto &[x0, x1, x2, x3, x4, x5, x6] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5, x6);
+    } else if constexpr (size == 8) {
+        auto &[x0, x1, x2, x3, x4, x5, x6, x7] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5, x6, x7);
+    } else if constexpr (size == 9) {
+        auto &[x0, x1, x2, x3, x4, x5, x6, x7, x8] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5, x6, x7, x8);
+    } else if constexpr (size == 10) {
+        auto &[x0, x1, x2, x3, x4, x5, x6, x7, x8, x9] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5, x6, x7, x8, x9);
+    } else if constexpr (size == 11) {
+        auto &[x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10);
+    } else if constexpr (size == 12) {
+        auto &[x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11);
+    } else if constexpr (size == 13) {
+        auto &[x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12);
+    } else if constexpr (size == 14) {
+        auto &[x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13] = value;
+        return std::forward_as_tuple(x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13);
+    } else {
+        static_assert (sizeof(_Tp) == 0, "The struct has too many members.");
+    }
+}
+
+} // namespace dark::reflect
diff --git a/include/synchronize.h b/include/synchronize.h
new file mode 100644
index 0000000..eed40d0
--- /dev/null
+++ b/include/synchronize.h
@@ -0,0 +1,59 @@
+#pragma once
+#include "hardware.h"
+#include "reflect.h"
+#include <array>
+
+namespace dark::hardware {
+
+struct Visitor {
+    template <typename _Tp>
+    static constexpr bool is_syncable_v =
+        requires(_Tp &val) { { val.sync() } -> std::same_as<void>; };
+
+    template <typename _Tp> requires is_syncable_v<_Tp> 
+    static void sync(_Tp &val) { val.sync(); }
+
+    template <typename _Tp, typename _Base>
+    static _Base &cast(_Tp &value) { return static_cast<_Base &>(value); }
+};
+
+template <typename ..._Base>
+struct SyncTags {};
+
+template <typename _Tp>
+static constexpr bool is_valid_tag_v = false;
+template <typename ..._Base>
+static constexpr bool is_valid_tag_v<SyncTags<_Base...>> = true;
+template <typename _Tp>
+concept has_valid_tag = is_valid_tag_v<typename _Tp::Tags>;
+
+template <typename _Tp>
+static constexpr bool is_std_array_v = std::is_array_v<_Tp>;
+template <typename _Tp, std::size_t _Nm>
+static constexpr bool is_std_array_v<std::array<_Tp, _Nm>> = true;
+
+template <typename _Tp>
+inline void sync_member(_Tp &value);
+
+template <typename _Tp, typename ..._Base>
+inline void sync_by_tag(_Tp &value, SyncTags<_Base...>) {
+    (sync_member(Visitor::cast<_Tp, _Base>(value)), ...);
+}
+
+template <typename _Tp>
+inline void sync_member(_Tp &value) {
+    if constexpr (is_std_array_v<_Tp>) {
+        for (auto &member : value) sync_member(member);
+    } else if constexpr (Visitor::is_syncable_v<_Tp>) {
+        Visitor::sync(value);
+    } else if constexpr (has_valid_tag<_Tp>) {
+        sync_by_tag(value, typename _Tp::Tags {});
+    } else if constexpr (std::is_aggregate_v<_Tp>) {
+        auto &&tuple = reflect::tuplify(value);
+        std::apply([](auto &...members) { (sync_member(members), ...); }, tuple);
+    } else {
+        static_assert(sizeof(_Tp) == 0, "This type is not syncable.");
+    }
+}
+
+} // namespace dark::hardware
diff --git a/include/target.h b/include/target.h
new file mode 100644
index 0000000..8daf92c
--- /dev/null
+++ b/include/target.h
@@ -0,0 +1,9 @@
+#pragma once
+#include <cstdint>
+
+namespace dark {
+
+using target_size_t = std::uint32_t;
+using target_ssize_t = std::int32_t;
+
+} // namespace dark
diff --git a/include/template.h b/include/template.h
new file mode 100644
index 0000000..e69de29