error[E0599]: no method named `f` found for type `fn(&u8)` in the current scope --> $DIR/issue-57362-1.rs:20:7 | LL | a.f(); | ^ method not found in `fn(&u8)` | = note: a is a function, perhaps you wish to call it = help: items from traits can only be used if the trait is implemented and in scope = note: the following trait defines an item `f`, perhaps you need to implement it: candidate #1: `Trait` error: aborting due to previous error For more information about this error, try `rustc --explain E0599`.