From 30a06186db0eb592ff719af8b8adc1b2651ee25d Mon Sep 17 00:00:00 2001
From: CHatingPython <chatingpython@kpgpmc.org>
Date: Tue, 1 Sep 2026 22:33:18 +0200
Subject: [PATCH] feat(furvm): introduce stack storage

Closes: #62
---
 furvm/include/furvm/executor.hpp | 38 ++++++++-------
 furvm/include/furvm/function.hpp |  1 -
 furvm/include/furvm/thing.hpp    | 72 +++++++++++++++++++++++++----
 furvm/src/executor.cpp           | 79 +++++++++++++++++++-------------
 4 files changed, 130 insertions(+), 60 deletions(-)

diff --git a/furvm/include/furvm/executor.hpp b/furvm/include/furvm/executor.hpp
index e269511..6ddeb2f 100644
--- a/furvm/include/furvm/executor.hpp
+++ b/furvm/include/furvm/executor.hpp
@@ -3,7 +3,8 @@
 
 #include "furvm/fwd.hpp"
 #include "furvm/module.hpp" // IWYU pragma: keep
-#include "furvm/thing.hpp"  // IWYU pragma: keep
+#include "furvm/stack.hpp"
+#include "furvm/thing.hpp" // IWYU pragma: keep
 
 #include <functional>
 #include <stack>
@@ -39,6 +40,8 @@ public:
     static constexpr executor_flags STATE_FLAGS = executor_flags::JustHit;
 
     using new_frame_callback = std::function<void(executor&)>;
+
+    using stack_thing = thing<stack_allocator>;
 public:
     /**
      * @brief Executor frame.
@@ -50,8 +53,8 @@ public:
         std::size_t position;  /**< Cursor to a current instruction in the bytecode. */
         std::size_t stackBase; /**< Snapshot of the stack size before this frame. */
 
-        thing_type*          returnType; /**< Return type. */
-        std::vector<thing<>> variables;  /**< Frame variables. */
+        thing_type*              returnType; /**< Return type. */
+        std::vector<stack_thing> variables;  /**< Frame variables. */
     };
 public:
     ~executor() = default;
@@ -131,27 +134,27 @@ public:
      * @param thing Thing.
      * @return The pushed handle.
      */
-    thing<>& push_thing(thing<>&& thing);
+    stack_thing& push_thing(stack_thing&& thing);
 
-    thing<>& push_thing(const thing<>& thing);
+    stack_thing& push_thing(const stack_thing& thing);
 
     /**
      * @brief Pops a thing from the stack.
      *
      * @return A handle to the popped thing.
      */
-    thing<> pop_thing();
+    stack_thing pop_thing();
 
     /**
      * @brief Returns the top thing on the stack.
      *
      * @return A handle to the top thing.
      */
-    thing<>& top_thing();
+    stack_thing& top_thing();
 
-    const thing<>& top_thing() const;
+    const stack_thing& top_thing() const;
 
-    const std::vector<thing<>>& stack() const { return m_stack; }
+    const std::vector<stack_thing>& stack() const { return m_stack; }
 public:
     /**
      * @brief Stores a thing in a frame variable.
@@ -159,7 +162,7 @@ public:
      * @param variable Id of the variable in which the handle will be put.
      * @param thing Thing handle.
      */
-    void store_thing(variable_t variable, const thing<>& thing);
+    void store_thing(variable_t variable, const stack_thing& thing);
 
     /**
      * @brief Stores a thing in a frame variable.
@@ -167,7 +170,7 @@ public:
      * @param variable Id of the variable in which the handle will be put.
      * @param thing Thing handle.
      */
-    void store_thing(variable_t variable, thing<>&& thing);
+    void store_thing(variable_t variable, stack_thing&& thing);
 
     /**
      * @brief Returns a thing stored in a variable.
@@ -175,9 +178,9 @@ public:
      * @param variable Id of the variable from which the handle will be fetched.
      * @return A handle stored in the variable.
      */
-    thing<>& load_thing(variable_t variable);
+    stack_thing& load_thing(variable_t variable);
 
-    const thing<>& load_thing(variable_t variable) const;
+    const stack_thing& load_thing(variable_t variable) const;
 public:
     /**
      * @brief Executes next instruction.
@@ -190,11 +193,12 @@ private:
 private:
     static bool compare_thing_types(const thing_type& lhs, const thing_type& rhs);
 private:
-    executor_flags m_flags = executor_flags::Done;
-    context*       m_context;
+    executor_flags          m_flags = executor_flags::Done;
+    context*                m_context;
+    furvm::stack<std::byte> m_stackStorage;
 
-    std::stack<frame>    m_frames;
-    std::vector<thing<>> m_stack;
+    std::stack<frame>        m_frames;
+    std::vector<stack_thing> m_stack;
 
     new_frame_callback m_newFrameCb = nullptr;
 };
diff --git a/furvm/include/furvm/function.hpp b/furvm/include/furvm/function.hpp
index 8177cc1..70f984b 100644
--- a/furvm/include/furvm/function.hpp
+++ b/furvm/include/furvm/function.hpp
@@ -1,7 +1,6 @@
 #ifndef FURVM_FUNCTION_HPP
 #define FURVM_FUNCTION_HPP
 
-#include "furlang/utility/hash.hpp"
 #include "furvm/fwd.hpp"
 #include "furvm/handle.hpp" // IWYU pragma: keep
 
diff --git a/furvm/include/furvm/thing.hpp b/furvm/include/furvm/thing.hpp
index 91429b9..2778f64 100644
--- a/furvm/include/furvm/thing.hpp
+++ b/furvm/include/furvm/thing.hpp
@@ -194,6 +194,9 @@ private:
 template <template <typename> typename Allocator>
 class thing final {
     friend class executor;
+
+    template <template <typename> class Other>
+    friend class thing;
 public:
     using allocator_type = Allocator<std::byte>; /**< Allocator type. */
 public:
@@ -206,7 +209,8 @@ public:
         thing_type type;
     };
 public:
-    thing() {}
+    thing(const allocator_type& allocator = {})
+      : m_allocator(allocator) {}
 
     /**
      * @brief Constructs a thing.
@@ -230,15 +234,15 @@ public:
      *
      * TODO: Reword the note above.
      */
-    static thing make_reference(const thing& owner) {
-        thing ref;
+    template <template <typename> class Other = Allocator>
+    static thing make_reference(const thing<Other>& owner, const allocator_type& allocator = {}) {
+        thing ref       = { allocator };
         ref.m_reference = true;
         ref.m_data      = owner.m_data;
         ref.m_type      = owner.m_type;
         ref.m_size      = owner.m_size;
         return ref;
     }
-
     /**
      * @brief Destructs a thing.
      */
@@ -247,7 +251,16 @@ public:
     /**
      * @brief Move constructor.
      */
-    thing(thing&& other) noexcept { *this = std::move(other); }
+    thing(thing&& other) noexcept
+      : m_reference(other.m_reference),
+        m_type(other.m_type),
+        m_size(other.m_size),
+        m_data(other.m_data),
+        m_allocator(other.m_allocator) {
+        other.m_type = nullptr;
+        other.m_data = nullptr;
+        other.m_size = 0;
+    }
 
     /**
      * @brief Move constructor.
@@ -266,7 +279,16 @@ public:
         return *this;
     }
 
-    thing(const thing& other) { *this = other; }
+    thing(const thing& other)
+      : m_reference(other.m_reference), m_size(other.m_size), m_allocator(other.m_allocator) {
+        if (m_reference) {
+            m_type = other.m_type;
+            m_data = other.m_data;
+            return;
+        }
+        allocate(other.type());
+        other.copy(*this);
+    }
 
     thing& operator=(const thing& other) {
         if (this == &other) return *this;
@@ -275,7 +297,38 @@ public:
 
         m_reference = other.m_reference;
         m_size      = other.m_size;
-        m_allocator = other.m_allocator;
+
+        if (m_reference) {
+            m_type = other.m_type;
+            m_data = other.m_data;
+            return *this;
+        }
+        allocate(other.type());
+        other.copy(*this);
+
+        return *this;
+    }
+
+    template <template <typename> class Other>
+    thing(const thing<Other>& other)
+      : m_reference(other.m_reference), m_size(other.m_size) {
+        if (m_reference) {
+            m_type = other.m_type;
+            m_data = other.m_data;
+            return;
+        }
+        allocate(other.type());
+        other.copy(*this);
+    }
+
+    template <template <typename> class Other>
+    thing& operator=(const thing<Other>& other) {
+        if (this == &other) return *this;
+
+        free();
+
+        m_reference = other.m_reference;
+        m_size      = other.m_size;
 
         if (m_reference) {
             m_type = other.m_type;
@@ -299,7 +352,8 @@ public:
         return res;
     }
 private:
-    void copy(thing<>& dst) const {
+    template <template <typename> class Other>
+    void copy(thing<Other>& dst) const {
         switch (m_type->type) {
         case thing_type::S8:
         case thing_type::S16:
@@ -499,7 +553,7 @@ public:
     thing at(thing_type::u64 index) const {
         if (!is(thing_type::Array)) throw bad_thing_access();
 
-        thing ref       = {};
+        thing ref       = { m_allocator };
         ref.m_reference = true;
         ref.m_size      = compute_size_na(*type().value.array.type);
 
diff --git a/furvm/src/executor.cpp b/furvm/src/executor.cpp
index 9697ed9..308e173 100644
--- a/furvm/src/executor.cpp
+++ b/furvm/src/executor.cpp
@@ -70,20 +70,22 @@ bool executor::compare_thing_types(const thing_type& lhs, const thing_type& rhs)
 }
 
 void executor::push_frame(const mod_h& mod, function function) {
+    m_stackStorage.push_frame();
+
     mod_h modInst = mod;
     while (function.type() == function_t::Import) {
         modInst  = m_context->at(function.imp().mod);
         function = *modInst->function_at(function.imp().function);
     }
 
-    auto                 signature = function.signature();
-    std::vector<thing<>> args;
+    auto                     signature = function.signature();
+    std::vector<stack_thing> args;
     args.reserve(signature.params.size());
     for (const auto& param : signature.params) {
         auto arg = pop_thing();
         if (compare_thing_types(arg.type(), *mod_to_thing_type(mod, *param)))
             throw std::runtime_error("function argument type mismatch");
-        args.push_back(std::move(arg));
+        args.emplace_back(std::move(arg));
     }
 
     struct thing_type* returnType = nullptr;
@@ -117,7 +119,7 @@ struct executor::frame executor::pop_frame() {
     if (m_frames.empty()) throw stack_underflow();
     struct executor::frame frame = m_frames.top();
     m_frames.pop();
-    std::optional<thing<>> returnValue;
+    std::optional<stack_thing> returnValue;
     if (frame.returnType != nullptr) {
         returnValue = pop_thing();
         if (returnValue->type() != *frame.returnType) throw std::runtime_error("function return type mismatch");
@@ -132,6 +134,8 @@ struct executor::frame executor::pop_frame() {
     }
     m_flags = m_flags & ~executor_flags::JustHit;
 
+    m_stackStorage.pop_frame();
+
     return frame;
 }
 
@@ -139,49 +143,49 @@ struct executor::frame executor::top_frame() const {
     return m_frames.top();
 }
 
-thing<>& executor::push_thing(thing<>&& thing) {
+executor::stack_thing& executor::push_thing(stack_thing&& thing) {
     return m_stack.emplace_back(std::move(thing));
 }
 
-thing<>& executor::push_thing(const thing<>& thing) {
+executor::stack_thing& executor::push_thing(const stack_thing& thing) {
     return m_stack.emplace_back(thing);
 }
 
-thing<> executor::pop_thing() {
+executor::stack_thing executor::pop_thing() {
     if (m_frames.top().stackBase >= m_stack.size()) throw stack_underflow();
     auto top = std::move(m_stack.back());
     m_stack.pop_back();
     return std::move(top);
 }
 
-thing<>& executor::top_thing() {
+executor::stack_thing& executor::top_thing() {
     if (m_frames.top().stackBase >= m_stack.size()) throw stack_underflow();
     return m_stack.back();
 }
 
-const thing<>& executor::top_thing() const {
+const executor::stack_thing& executor::top_thing() const {
     if (m_frames.top().stackBase >= m_stack.size()) throw stack_underflow();
     return m_stack.back();
 }
 
-void executor::store_thing(variable_t variable, const thing<>& thing) {
+void executor::store_thing(variable_t variable, const stack_thing& thing) {
     auto& frame = m_frames.top();
     if (frame.variables.size() <= variable) frame.variables.resize(variable + 1);
     frame.variables[variable] = thing;
 }
 
-void executor::store_thing(variable_t variable, thing<>&& thing) {
+void executor::store_thing(variable_t variable, stack_thing&& thing) {
     auto& frame = m_frames.top();
     if (frame.variables.size() <= variable) frame.variables.resize(variable + 1);
     frame.variables[variable] = std::move(thing);
 }
 
-thing<>& executor::load_thing(variable_t variable) {
+executor::stack_thing& executor::load_thing(variable_t variable) {
     auto& frame = m_frames.top();
     return frame.variables[variable];
 }
 
-const thing<>& executor::load_thing(variable_t variable) const {
+const executor::stack_thing& executor::load_thing(variable_t variable) const {
     const auto& frame = m_frames.top();
     return frame.variables[variable];
 }
@@ -204,38 +208,45 @@ void executor::step() {
     switch (instr.type) {
     case instruction_t::NoOperation: break;
     case instruction_t::PushS8: {
-        push_thing({ (struct thing_type){ thing_type::S8 } }).get<thing_type::s8>() = instr.arg.s8;
+        push_thing({ (struct thing_type){ thing_type::S8 }, { m_stackStorage } }).get<thing_type::s8>() = instr.arg.s8;
     } break;
     case instruction_t::PushU8: {
-        push_thing({ (struct thing_type){ thing_type::U8 } }).get<thing_type::u8>() = instr.arg.u8;
+        push_thing({ (struct thing_type){ thing_type::U8 }, { m_stackStorage } }).get<thing_type::u8>() = instr.arg.u8;
     } break;
     case instruction_t::PushS16: {
-        push_thing({ (struct thing_type){ thing_type::S16 } }).get<thing_type::s16>() = instr.arg.s16;
+        push_thing({ (struct thing_type){ thing_type::S16 }, { m_stackStorage } }).get<thing_type::s16>() =
+            instr.arg.s16;
     } break;
     case instruction_t::PushU16: {
-        push_thing({ (struct thing_type){ thing_type::U16 } }).get<thing_type::u16>() = instr.arg.u16;
+        push_thing({ (struct thing_type){ thing_type::U16 }, { m_stackStorage } }).get<thing_type::u16>() =
+            instr.arg.u16;
     } break;
     case instruction_t::PushS32: {
-        push_thing({ (struct thing_type){ thing_type::S32 } }).get<thing_type::s32>() = instr.arg.s8; // NOLINT
+        push_thing({ (struct thing_type){ thing_type::S32 }, { m_stackStorage } }).get<thing_type::s32>() =
+            instr.arg.s8; // NOLINT
     } break;
     case instruction_t::PushU32: {
-        push_thing({ (struct thing_type){ thing_type::U32 } }).get<thing_type::u32>() =
+        push_thing({ (struct thing_type){ thing_type::U32 }, { m_stackStorage } }).get<thing_type::u32>() =
             static_cast<thing_type::u32>(instr.arg.u8);
     } break;
     case instruction_t::PushConstant: {
         auto constant = frame.mod->constant_at(instr.arg.u16);
         switch (constant.type) {
         case constant::S32:
-            push_thing({ (struct thing_type){ thing_type::S32 } }).get<thing_type::s32>() = constant.s32; // NOLINT
+            push_thing({ (struct thing_type){ thing_type::S32 }, { m_stackStorage } }).get<thing_type::s32>() =
+                constant.s32; // NOLINT
             break;
         case constant::U32:
-            push_thing({ (struct thing_type){ thing_type::U32 } }).get<thing_type::u32>() = constant.u32; // NOLINT
+            push_thing({ (struct thing_type){ thing_type::U32 }, { m_stackStorage } }).get<thing_type::u32>() =
+                constant.u32; // NOLINT
             break;
         case constant::S64:
-            push_thing({ (struct thing_type){ thing_type::S64 } }).get<thing_type::s64>() = constant.s64; // NOLINT
+            push_thing({ (struct thing_type){ thing_type::S64 }, { m_stackStorage } }).get<thing_type::s64>() =
+                constant.s64; // NOLINT
             break;
         case constant::U64:
-            push_thing({ (struct thing_type){ thing_type::U64 } }).get<thing_type::u64>() = constant.u64; // NOLINT
+            push_thing({ (struct thing_type){ thing_type::U64 }, { m_stackStorage } }).get<thing_type::u64>() =
+                constant.u64; // NOLINT
             break;
         case constant::String: throw std::runtime_error("unimplemented");
         default: throw std::runtime_error("invalid constant");
@@ -246,7 +257,7 @@ void executor::step() {
         if (type.type != thing_type::Array || type.value.array.type == nullptr || type.value.array.type == &type)
             throw std::runtime_error("invalid array type");
 
-        auto& array = push_thing({ type });
+        auto& array = push_thing({ type, { m_stackStorage } });
 
         if (type.value.array.size == 0) {
             auto         sizeThing = pop_thing();
@@ -281,7 +292,7 @@ void executor::step() {
         push_thing(top_thing());
     } break;
     case instruction_t::Reference: {
-        push_thing(thing<>::make_reference(pop_thing()));
+        push_thing(stack_thing::make_reference(pop_thing(), { m_stackStorage }));
     } break;
     case instruction_t::Add: {
         auto rhs = pop_thing();
@@ -340,12 +351,13 @@ void executor::step() {
     } break;
     case instruction_t::Pointerof: {
         auto thing = pop_thing();
-        push_thing({ (struct thing_type){ thing_type::Ptr, m_context->tt_store().at(thing.type().id) } }).get<void*>() =
-            thing.raw();
+        push_thing(
+            { (struct thing_type){ thing_type::Ptr, m_context->tt_store().at(thing.type().id) }, { m_stackStorage } })
+            .get<void*>() = thing.raw();
     } break;
     case instruction_t::Sizeof: {
         auto  thing = pop_thing();
-        auto& size  = push_thing({ (struct thing_type){ thing_type::U64 } });
+        auto& size  = push_thing({ (struct thing_type){ thing_type::U64 }, { m_stackStorage } });
         switch (thing.type().type) {
         case thing_type::S8:
         case thing_type::S16:
@@ -368,20 +380,21 @@ void executor::step() {
         }
     } break;
     case instruction_t::Lengthof: {
-        auto thing                                                                    = pop_thing();
-        push_thing({ (struct thing_type){ thing_type::U64 } }).get<thing_type::u64>() = thing.length();
+        auto thing = pop_thing();
+        push_thing({ (struct thing_type){ thing_type::U64 }, { m_stackStorage } }).get<thing_type::u64>() =
+            thing.length();
     } break;
     case instruction_t::Load: {
-        push_thing(std::move(thing<>::make_reference(load_thing(instr.arg.u16))));
+        push_thing(std::move(stack_thing::make_reference(load_thing(instr.arg.u16), { m_stackStorage })));
     } break;
     case instruction_t::Store: {
         store_thing(instr.arg.u16, std::move(pop_thing()));
     } break;
     case instruction_t::LoadGlobal: {
-        push_thing(thing<>::make_reference(frame.mod->load_global_variable(instr.arg.u16)));
+        push_thing(stack_thing::make_reference(frame.mod->load_global_variable(instr.arg.u16), { m_stackStorage }));
     } break;
     case instruction_t::StoreGlobal: {
-        frame.mod->store_global_variable(instr.arg.u16, std::move(pop_thing()));
+        frame.mod->store_global_variable(instr.arg.u16, pop_thing());
     } break;
     case instruction_t::Call: {
         push_frame(frame.mod, *frame.mod->function_at(instr.arg.u16));