error[E0277]: `RefCell` cannot be shared between threads safely --> $DIR/issue-7364.rs:4:15 | LL | static boxed: Box> = Box::new(RefCell::new(0)); | ^^^^^^^^^^^^^^^^^^^ `RefCell` cannot be shared between threads safely | = help: the trait `Sync` is not implemented for `RefCell` = note: if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` instead = note: required for `Unique>` to implement `Sync` = note: required because it appears within the type `Box>` = note: shared static variables must have a type that implements `Sync` error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.