error[E0393]: the type parameter `T` must be explicitly specified --> $DIR/issue-22370.rs:3:14 | LL | trait A {} | --------------- type parameter `T` must be specified for this LL | LL | fn f(a: &dyn A) {} | ^ help: set the type parameter to the desired type: `A` | = note: because of the default `Self` reference, type parameters must be specified on object types error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0393`.