use std::collections::hash_map::DefaultHasher;
use std::hash::Hash;

pub trait Hash2 {
    fn hash2(&self, state: &mut DefaultHasher);
}

pub fn doit(h: &mut DefaultHasher, a: &dyn Hash2, b: &dyn Hash2) -> bool {
    a.hash2(h) == b.hash2(h)
}

impl<T> Hash2 for T
where
    T: Hash,
{
    fn hash2(&self, state: &mut DefaultHasher) {
        self.hash(state)
    }
}

#[test]
fn check() {
    let mut hasher = DefaultHasher::new();
    assert!(doit(&mut hasher, &5, &5));
    assert_false!(doit(&mut hasher, &5, &5.0));
}