error[E0596]: cannot borrow immutable indexed content as mutable --> $DIR/issue-41726.rs:15:9 | LL | things[src.as_str()].sort(); //~ ERROR cannot borrow immutable | ^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable | = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap>` error: aborting due to previous error For more information about this error, try `rustc --explain E0596`.