Currently UnsafeCell does not implement Copy. It would be beneficial if it could, for at least two reasons:

• Easier initialization of fixed arrays, e g: [UnsafeCell::new(0i32); 75]
• It enables people to make cell-like types which are Copy.

AFAIK, there are no disadvantages for UnsafeCell to implement Copy.

Note: the reason people can't just copy-and-paste the code for UnsafeCell to make their own variant with copy semantics, is that UnsafeCell is a #[lang="unsafe_cell"]: "The UnsafeCell<T> type is the only legal way to obtain aliasable data that is considered mutable. In general, transmuting an &T type into an &mut T is considered undefined behavior."