error[E0594]: cannot assign to `v.v`, which is behind a `&` reference --> $DIR/suggest-mut-method-for-loop-hashmap.rs:17:9 | LL | for (_k, v) in map.iter() { | ---------- | | | | | help: use mutable method: `iter_mut()` | this iterator yields `&` references ... LL | v.v += 1; | ^^^^^^^^ `v` is a `&` reference, so the data it refers to cannot be written error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0594`.