Macro debug_unreachable::debug_unreachable

macro_rules! debug_unreachable {
    () => { ... };
    ($e:expr) => { ... };
}

panic!() in debug builds, optimization hint in release.

Example:

use debug_unreachable::debug_unreachable;

fn main() {
    if 0 > 100 {
        // Can't happen!
        unsafe { debug_unreachable!() }
    } else {
        println!("Good, 0 <= 100.");
    }
}