1 files changed, 55 insertions, 0 deletions

diff --git a/src/allocator.hpp b/src/allocator.hpp
new file mode 100644
index 0000000..fa48c46
--- /dev/null
+++ b/src/allocator.hpp
@@ -0,0 +1,55 @@
+#pragma once
+
+#include "compat.hpp"
+
+// #################################################################################################
+
+namespace lanes {
+
+    // everything we need to provide to lua_newstate()
+    class AllocatorDefinition
+    {
+        public:
+        // xxh64 of string "kAllocatorVersion_1" generated at https://www.pelock.com/products/hash-calculator
+        static constexpr uintptr_t kAllocatorVersion{ static_cast<uintptr_t>(0xCF9D321B0DFB5715ull) };
+        uintptr_t version{ kAllocatorVersion };
+        lua_Alloc allocF{ nullptr };
+        void* allocUD{ nullptr };
+
+        [[nodiscard]] static void* operator new(size_t const size_) noexcept = delete; // can't create one outside of a Lua state
+        [[nodiscard]] static void* operator new(size_t const size_, lua_State* const L_) noexcept { return lua_newuserdatauv(L_, size_, UserValueCount{ 0 }); }
+        // always embedded somewhere else or "in-place constructed" as a full userdata
+        // can't actually delete the operator because the compiler generates stack unwinding code that could call it in case of exception
+        static void operator delete([[maybe_unused]] void* const p_, [[maybe_unused]] lua_State* const L_) {}
+
+        AllocatorDefinition(uintptr_t const version_, lua_Alloc const allocF_, void* const allocUD_) noexcept
+        : version{ version_ }
+        , allocF{ allocF_ }
+        , allocUD{ allocUD_ }
+        {
+        }
+
+        // rule of 5
+        AllocatorDefinition() = default;
+        AllocatorDefinition(AllocatorDefinition const& rhs_) = default;
+        AllocatorDefinition(AllocatorDefinition&& rhs_) = default;
+        AllocatorDefinition& operator=(AllocatorDefinition const& rhs_) = default;
+        AllocatorDefinition& operator=(AllocatorDefinition&& rhs_) = default;
+
+        void initFrom(lua_State* const L_)
+        {
+            allocF = lua_getallocf(L_, &allocUD);
+        }
+
+        void* alloc(size_t const nsize_)
+        {
+            return allocF(allocUD, nullptr, 0, nsize_);
+        }
+
+        void free(void* const ptr_, size_t const osize_)
+        {
+            std::ignore = allocF(allocUD, ptr_, osize_, 0);
+        }
+    };
+
+} // namespace lanes