1 error[E0599]: no method named `f` found for type `fn(&u8)` in the current scope
2 --> $DIR/issue-57362-1.rs:20:7
7 = note: a is a function, perhaps you wish to call it
8 = help: items from traits can only be used if the trait is implemented and in scope
9 = note: the following trait defines an item `f`, perhaps you need to implement it:
12 error: aborting due to previous error
14 For more information about this error, try `rustc --explain E0599`.