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