error[E0515]: cannot return value referencing function parameter `y` --> $DIR/issue-81584.rs:5:22 | LL | .map(|y| y.iter().map(|x| x + 1)) | -^^^^^^^^^^^^^^^^^^^^^^ | | | returns a value referencing data owned by the current function | `y` is borrowed here | = help: use `.collect()` to allocate the iterator error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0515`.