error[E0393]: the type parameter `T` must be explicitly specified --> $DIR/E0393.rs:3:47 | LL | trait A {} | --------------- type parameter `T` must be specified for this LL | LL | fn together_we_will_rule_the_galaxy(son: &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 previous error For more information about this error, try `rustc --explain E0393`.