1 This error occurs because you tried to mutably borrow a non-mutable variable.
3 Erroneous code example:
7 let y = &mut x; // error: cannot borrow mutably
10 In here, `x` isn't mutable, so when we try to mutably borrow it in `y`, it
11 fails. To fix this error, you need to make `x` mutable:
15 let y = &mut x; // ok!