error[E0277]: the trait bound `Self: Eq` is not satisfied --> $DIR/wf-trait-default-fn-arg.rs:11:23 | LL | fn bar(&self, x: &Bar) { | ^^^^^^^^^ the trait `Eq` is not implemented for `Self` | note: required by a bound in `Bar` --> $DIR/wf-trait-default-fn-arg.rs:8:14 | LL | struct Bar { value: Box } | ^^ required by this bound in `Bar` help: consider further restricting `Self` | LL | fn bar(&self, x: &Bar) where Self: Eq { | ++++++++++++++ error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.