1 files changed, 47 insertions, 0 deletions

diff --git a/src/allocator.h b/src/allocator.h
new file mode 100644
index 0000000..9a9c245
--- /dev/null
+++ b/src/allocator.h
@@ -0,0 +1,47 @@
+#pragma once
+
+// #################################################################################################
+
+// 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 size_) noexcept = delete; // can't create one outside of a Lua state
+    [[nodiscard]] static void* operator new(size_t size_, lua_State* L_) noexcept { return lua_newuserdatauv(L_, size_, 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* p_, [[maybe_unused]] lua_State* L_) {}
+
+    AllocatorDefinition(uintptr_t const version_, lua_Alloc const allocF_, void* const allocUD_) noexcept
+    : version{ version_ }
+    , allocF{ allocF_ }
+    , allocUD{ allocUD_ }
+    {
+    }
+    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* L_)
+    {
+        allocF = lua_getallocf(L_, &allocUD);
+    }
+
+    void* alloc(size_t nsize_)
+    {
+        return allocF(allocUD, nullptr, 0, nsize_);
+    }
+
+    void free(void* ptr_, size_t osize_)
+    {
+        std::ignore = allocF(allocUD, ptr_, osize_, 0);
+    }
+};