E0502 — Cannot Borrow as Mutable Because Also Borrowed as Immutable

Cause di questo errore

Rust enforces that you cannot have a mutable reference and an immutable reference to the same data at the same time. The immutable borrow is still in use when you try to take a mutable borrow.

Come correggerlo

Restructure the code so the immutable borrow ends before the mutable borrow begins. Clone the data if you need independent copies. Use a block to limit the scope of the immutable borrow.

let mut v = vec![1, 2];
let r = &v[0];
v.push(3);
println!("{}", r);