Macro static_assertions::const_assert_eq

macro_rules! const_assert_eq {
    ($x:expr, $($xs:expr),+ $(,)*) => { ... };
    ($label:ident; $x:expr, $($xs:expr),+ $(,)*) => { ... };
}

Asserts that constants are equal in value.

Examples

Works as a shorthand for const_assert!(a == b):

const TWO: usize = 2;
const_assert_eq!(two; TWO * TWO, TWO + TWO, 4);

fn main() {
    const NUM: usize = 32;
    const_assert_eq!(NUM + NUM, 64);
}

Just because 2 × 2 = 2 + 2 doesn’t mean it holds true for other numbers:

const_assert_eq!(4 + 4, 4 * 4);