Add arena to furlang

Signed-off-by: CHatingPython <chatingpython@gmail.com>

furlang/include/furlang/arena.hpp

@@ -0,0 +1,48 @@
+#ifndef FURLANG_ARENA_HPP
+#define FURLANG_ARENA_HPP
+
+#include <cstddef>
+#include <cstdint>
+
+namespace furlang {
+
+class arena {
+private:
+    struct region {
+        using value_type = std::uintptr_t;
+
+        static region* create(std::size_t capacity);
+
+        region*     next;
+        std::size_t capacity;
+        std::size_t used;
+        value_type  storage[];
+
+        std::size_t free() const { return capacity - used; }
+    };
+public:
+    arena(std::size_t minCapacity = 4 * 1024ULL);
+    ~arena();
+
+    arena(arena&& other) noexcept;
+    arena(const arena&) = delete;
+    arena& operator=(arena&& other) noexcept;
+    arena& operator=(const arena&) = delete;
+public:
+    template <typename T>
+    T* allocate(std::size_t count = 1) {
+        return reinterpret_cast<T*>(allocate(sizeof(T), count));
+    }
+
+    void reset();
+private:
+    void* allocate(std::size_t size, std::size_t count);
+private:
+    std::size_t m_minCapacity;
+    region*     m_head = nullptr;
+    region*     m_tail = nullptr;
+};
+
+} // namespace furlang
+
+#endif // FURLANG_ARENA_HPP