こう書くと、 fn main() { let mut a = [1, 2, 3, 4, 5]; let x = &mut a[3..a.len()]; println!("{:?}", x); } こう怒られる。 error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable --> src/main.rs:3:23 | 3 | let x = …