Cannot borrow data in a & reference as mutable

A mutable reference is a borrow to any type mut T , allowing mutation of T through that reference. The below code illustrates the example of a mutable variable and then mutating its value through a mutable reference ref_i . fn main() {

Mutable References First we change s to be mut . Then we create a mutable reference with &mut s where we call the change function, and update the function signature to accept a mutable reference with some_string: &mut String . This makes it very clear that the change function will mutate the value it borrows.

You can get mutable references to all elements at the same time: lst. iter_mut(). collect::<Vec<_>>() . This works because each mutable reference from the iterator will be distinct.