How to operate on 2 mutable slices of a Rust array?

Is there anything unsafe about having two mutable references to nonoverlapping slices of the same array?

There isn't, but Rust's type system cannot currently detect that you're taking mutable references to two non-overlapping parts of a slice. As this is a common use case, Rust provides a safe function to do exactly what you want: std::slice::split_at_mut.

fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T])

Divides one &mut into two at an index.

The first will contain all indices from [0, mid) (excluding the index mid itself) and the second will contain all indices from [mid, len) (excluding the index len itself).

The final code is:

fn main() {
    let mut mem : [i32; 2048] = [1; 2048];
    let (mut array0, mut array1) = mem[..].split_at_mut(768);
    array0[0] = 4;
    println!("{:?} {:?}", array0[0], array1[0]);
}

Wow that was such a perfect match. Thanks for finding this!