error[E0038]: the trait alias `BB` cannot be made into an object --> $DIR/self-in-const-generics.rs:9:16 | LL | fn foo(x: &dyn BB) {} | ^^ | = note: it cannot use `Self` as a type parameter in a supertrait or `where`-clause error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0038`.