Creating two dimensional arrays in Rust

Question

In Rust 1.0, the following works:

let mut state = [[0u8; 4]; 6];
state[0][1] = 42;

Note that the length of the interior segment is an integral part of the type. For example, you can reference (and pass) state as follows:

let a: &[[u8; 4]] = &state;

but not without specifying the fixed length of the sub-array. If you need variable length sub-arrays you may need to do something like this:

let x: [Box<[u8]>; 3] = [
    Box::new([1, 2, 3]),
    Box::new([4]), 
    Box::new([5, 6])
];
let y: &[Box<[u8]>] = &x;