#![feature(const_fn)]

const fn align_of<T>(_: &T) -> usize {
    ::std::mem::size_of::<T>()
}

// fails to compile if the types of $x and $y don't have the same alignment
macro_rules! assert_eq_align {
    ($x:expr, $y:expr) => (
        // don't actually evaluate at runtime
        if false { const_assert!(align_of(&$x) == align_of(&$y)); }
        ($x, $y)
    )
}

// copied from static_assertions crate
macro_rules! const_assert {
    ($($xs:expr),+ $(,)*) => {
        #[allow(unknown_lints, eq_op)]
        let _ = [(); 0 - !($($xs)&&+) as usize];
    };
    ($label:ident; $($xs:tt)+) => {
        #[allow(dead_code, non_snake_case)]
        fn $label() { const_assert!($($xs)+); }
    };
}

fn main() {
    let (a, b) = assert_eq_align!(0u8, 0u16);
}