use std::hash::Hasher;

#[derive(Default, Clone, Copy, PartialEq, Eq)]
pub struct NoHash(Option<u64>);

impl Hasher for NoHash {
    fn write_u64(&mut self, i: u64) {
        if self.0.is_some() {
            panic!("called write_u64 twice")
        } else {
            self.0 = Some(i);
        }
    }

    fn write(&mut self, _: &[u8]) {
        unreachable!()
    }

    fn finish(&self) -> u64 {
        self.0.unwrap()
    }
}