error[E0277]: expected a `Fn<(char,)>` closure, found `char` --> $DIR/root-obligation.rs:6:38 | LL | .filter(|c| "aeiou".contains(c)) | -------- ^ expected an `Fn<(char,)>` closure, found `char` | | | required by a bound introduced by this call | = help: the trait `Fn<(char,)>` is not implemented for `char` = note: required for `&char` to implement `FnOnce<(char,)>` = note: required for `&char` to implement `Pattern<'_>` note: required by a bound in `core::str::::contains` --> $SRC_DIR/core/src/str/mod.rs:LL:COL help: consider dereferencing here | LL | .filter(|c| "aeiou".contains(*c)) | + error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.