error[E0599]: the method `is_subset` exists for reference `&HashSet`, but its trait bounds were not satisfied --> $DIR/issue-35677.rs:7:10 | LL | this.is_subset(other) | ^^^^^^^^^ method cannot be called on `&HashSet` due to unsatisfied trait bounds | = note: the following trait bounds were not satisfied: `T: Eq` `T: Hash` help: consider restricting the type parameters to satisfy the trait bounds | LL | fn is_subset(this: &HashSet, other: &HashSet) -> bool where T: Eq, T: Hash { | ++++++++++++++++++++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0599`.