RefCell uses UnsafeCell inside. Everything that does mutation, under shared ownership, has UnsafeCell somewhere -- IIRC this is or was a requirement to guarante

RefCell uses UnsafeCell inside. Everything that does mutation, under shared ownership, has UnsafeCell somewhere -- IIRC this is or was a requirement to guarantee the compiler won't do certain optimizations. > but it's not Rust That's why I stipulated Rust without UnsafeCell.