error[E0594]: cannot assign to `t.v`, which is behind a `&` reference --> $DIR/suggest-mut-method-for-loop-closure.rs:15:13 | LL | for mut t in buzz.values() { | ------------- | | | | | help: use mutable method: `values_mut()` | this iterator yields `&` references ... LL | t.v += 1; | ^^^^^^^^ `t` is a `&` reference, so the data it refers to cannot be written error: aborting due to previous error For more information about this error, try `rustc --explain E0594`.