| A variable was borrowed as mutable more than once. |
| |
| Erroneous code example: |
| |
| ```compile_fail,E0499 |
| let mut i = 0; |
| let mut x = &mut i; |
| let mut a = &mut i; |
| x; |
| // error: cannot borrow `i` as mutable more than once at a time |
| ``` |
| |
| Please note that in Rust, you can either have many immutable references, or one |
| mutable reference. For more details you may want to read the |
| [References & Borrowing][references-and-borrowing] section of the Book. |
| |
| [references-and-borrowing]: https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html |
| |
| Example: |
| |
| ``` |
| let mut i = 0; |
| let mut x = &mut i; // ok! |
| |
| // or: |
| let mut i = 0; |
| let a = &i; // ok! |
| let b = &i; // still ok! |
| let c = &i; // still ok! |
| b; |
| a; |
| ``` |
