error[E0277]: expected a `FnMut<(char,)>` closure, found `u8` --> $DIR/assoc-fn-bound-root-obligation.rs:2:20 | LL | s.strip_suffix(b'\n').unwrap_or(s) | ------------ ^^^^^ expected an `FnMut<(char,)>` closure, found `u8` | | | required by a bound introduced by this call | = help: the trait `FnMut<(char,)>` is not implemented for `u8` = help: the following other types implement trait `Pattern<'a>`: &'b String &'b [char; N] &'b [char] &'b str &'c &'b str [char; N] char = note: required because of the requirements on the impl of `Pattern<'_>` for `u8` error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.