error[E0282]: type annotations needed --> $DIR/unconstrained-ref.rs:6:5 | LL | S { o: &None }; | ^^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the struct `S` | help: consider specifying the generic argument | LL | S:: { o: &None }; | +++++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0282`.