Send + Sync are automatically implemented for a type X if all of X's constituents are also Send + Sync. In practice, this means that unless you're using unsafe

Send + Sync are automatically implemented for a type X if all of X's constituents are also Send + Sync. In practice, this means that unless you're using unsafe code, Cell/RefCell or Rc, then the Right Thing will just happen automatically. If you are using Cell/RefCell/Rc/unsafe, then you need to think carefully about your synchronization story anyway, so it's typically not something you just forget to do. For more details, see: https://doc.rust-lang.org/std/marker/trait.Sync.html https://doc.rust-lang.org/std/marker/trait.Sync.html and https://doc.rust-lang.org/std/marker/trait.Send.html https://doc.rust-lang.org/std/marker/trait.Send.html