Comment by flohofwoe

> Destructors are not deallocators, they are supposed to set the object field in an invalid state.

A typical arena allocator would just reset an offset to zero when the arena is 'freed' without calling any object destructors, and the allocator wouldn't actually have any type information about the objects allocated in the arena (of course you could also write an allocator which registers a destructor function with each allocation, and which would be called before the arena is reset):

    bla_t* bla = arena_alloc(arena, alignment, size, destructor_func);

For C++ style RAII it probably makes more sense to use placement-new, and call the destructor manually to 'invalidate' the object without recycling its memory (the memory would only be recycled once the arena allocator is reset).