Assert equal type size in Rust

assert_eq_size.rs

use std::mem::transmute;

macro_rules! assert_eq_size {
    ($x:ty, $($xs:ty),+ $(,)*) => {
        $(let _ = transmute::<$x, $xs>;)+
    };
    ($label:ident; $($rest:tt)+) => {
        #[allow(dead_code, non_snake_case)]
        fn $label() {
            assert_eq_size!($($rest)+);
        }
    };
}

assert_eq_size! { some_sizes;
    [u8; 4],
    (u16, u16),
    u32,
}

fn main() {
    // Change me to any other number
    const N: usize = 2;

    assert_eq_size!(u32, [u16; N]);
}

This gist is used as an example within https://nikolaivazquez.com/posts/programming/rust-static-assertions/