1 error[E0277]: expected a `std::ops::FnMut<(_, char)>` closure, found `()`
2 --> $DIR/issue-23966.rs:12:16
4 LL | "".chars().fold(|_, _| (), ());
5 | ^^^^ expected an `FnMut<(_, char)>` closure, found `()`
7 = help: the trait `std::ops::FnMut<(_, char)>` is not implemented for `()`
9 error: aborting due to previous error
11 For more information about this error, try `rustc --explain E0277`.