From a05e4c88a1e21a177b6dad948f6c9f5369ce9cea Mon Sep 17 00:00:00 2001
From: Sinan <karakaya.sinan@proton.me>
Date: Sun, 10 Aug 2025 08:54:02 +0200
Subject: [PATCH] Feat: added support for std::allocator (#65)

* feat(memory): added arena_allocator for STL data types support
* fix(memory): fixed arena_allocate offset compute
---
 core/memory/arena.cpp         |  4 +--
 core/memory/arena_allocator.h | 68 +++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 2 deletions(-)
 create mode 100644 core/memory/arena_allocator.h

diff --git a/core/memory/arena.cpp b/core/memory/arena.cpp
index 2ea2bcf..46e7025 100644
--- a/core/memory/arena.cpp
+++ b/core/memory/arena.cpp
@@ -31,8 +31,8 @@ memory::arena_t memory::arena_init(size_t capacity)
 const void* memory::arena_allocate(memory::arena_t* arena, const std::size_t size)
 {
     ASSERT(arena != nullptr);
-    ASSERT(arena->size + size < arena->capacity);
-    const void* const data = &arena->data + arena->size;
+    ASSERT(arena->size + size <= arena->capacity);
+    const void* const data = static_cast<uint8_t*>(arena->data) + arena->size;
     arena->size += size;
     return data;
 }
diff --git a/core/memory/arena_allocator.h b/core/memory/arena_allocator.h
new file mode 100644
index 0000000..a4a3f3c
--- /dev/null
+++ b/core/memory/arena_allocator.h
@@ -0,0 +1,68 @@
+#ifndef POUND_ARENA_ALLOCATOR_H
+#define POUND_ARENA_ALLOCATOR_H
+
+#include <cstddef>
+#include <memory>
+#include "arena.h"
+
+namespace memory
+{
+    /**
+    @brief An STL-compatible allocator that uses a custom arena for memory management.
+    
+    This allocator allows STL containers (such as std::vector) to allocate memory from a user-provided arena,
+    enabling efficient bulk allocation and deallocation patterns. The arena must provide an `arena_allocate` function.
+    
+    @tparam T Type of object to allocate.
+    
+    @code
+    memory::arena_t my_arena = memory::arena_init(4096);
+    memory::arena_allocator<int> alloc(&my_arena);
+    
+    std::vector<int, memory::arena_allocator<int>> vec(alloc);
+    vec.push_back(42);
+    // ...
+    memory::arena_reset(&my_arena); // Frees all allocations in the arena
+    @endcode
+    
+    @note The deallocate function is a no-op; memory is managed by the arena.
+    
+    @see arena_t
+    @see arena_allocate
+    */
+    template <typename T>
+    struct arena_allocator {
+        using value_type = T;
+
+        arena_t* arena;
+
+        arena_allocator(arena_t* a) noexcept : arena(a) {}
+        
+        template <typename U>
+        arena_allocator(const arena_allocator<U>& other) noexcept : arena(other.arena) {}
+
+        T* allocate(std::size_t n) {
+            return static_cast<T*>(const_cast<void*>(arena_allocate(arena, n * sizeof(T))));
+        }
+
+        void deallocate(T*, std::size_t) noexcept {
+            // noop since memory should be freed by arena
+        }
+
+        template <typename U>
+        struct rebind { using other = arena_allocator<U>; };
+    };
+
+    template <typename T, typename U>
+    inline bool operator==(const arena_allocator<T>& a, const arena_allocator<U>& b) {
+        return a.arena == b.arena;
+    }
+
+    template <typename T, typename U>
+    inline bool operator!=(const arena_allocator<T>& a, const arena_allocator<U>& b) {
+        return a.arena != b.arena;
+    }
+
+}
+
+#endif // POUND_ARENA_ALLOCATOR_H
\ No newline at end of file