expectation.rs

trait Expectation<T> {
    fn expected(self, msg: &str) -> T;
}

impl<T> Expectation<T> for Option<T> {
    fn expected(self, msg: &str) -> T {
        match self {
            Some(val) => val,
            _ => expectation_failed(msg),
        }
    }
}

impl<T,E> Expectation<T> for Result<T,E> {
    fn expected(self, msg: &str) -> T {
        match self {
            Ok(val) => val,
            _ => expectation_failed(msg),
        }
    }
}

#[inline(never)]
#[cold]
fn expectation_failed(msg: &str) -> ! {
    panic!("expected {}", msg)
}