Macro debug_unreachable

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

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

This is equivalent to core::unreachable in debug builds, and core::hint::unreachable_unchecked in release builds.

Example:

use debug_unreachable::debug_unreachable;

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