error[E0277]: `RefCell<()>` cannot be shared between threads safely --> $DIR/suggest-ref-cell.rs:6:20 | LL | require_sync::>(); | ^^^^^^^^^^^^^^^^^^^^^^ `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 by a bound in `require_sync` --> $DIR/suggest-ref-cell.rs:1:20 | LL | fn require_sync() {} | ^^^^ required by this bound in `require_sync` error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.