error[E0599]: no method named `is_empty` found for struct `Foo` in the current scope --> $DIR/method-suggestion-no-duplication.rs:7:15 | LL | struct Foo; | ---------- method `is_empty` not found for this struct ... LL | foo(|s| s.is_empty()); | ^^^^^^^^ method not found in `Foo` | = help: items from traits can only be used if the trait is implemented and in scope = note: the following trait defines an item `is_empty`, perhaps you need to implement it: candidate #1: `ExactSizeIterator` error: aborting due to previous error For more information about this error, try `rustc --explain E0599`.