library/std/tests/eq-multidispatch.rs

#[derive(PartialEq, Debug)]
struct Bar;
#[derive(Debug)]
struct Baz;
#[derive(Debug)]
struct Foo;
#[derive(Debug)]
struct Fu;

impl PartialEq for Baz {
    fn eq(&self, _: &Baz) -> bool {
        true
    }
}

impl PartialEq<Fu> for Foo {
    fn eq(&self, _: &Fu) -> bool {
        true
    }
}

impl PartialEq<Foo> for Fu {
    fn eq(&self, _: &Foo) -> bool {
        true
    }
}

impl PartialEq<Bar> for Foo {
    fn eq(&self, _: &Bar) -> bool {
        false
    }
}

impl PartialEq<Foo> for Bar {
    fn eq(&self, _: &Foo) -> bool {
        false
    }
}

#[test]
fn eq_multidispatch() {
    assert!(Bar != Foo);
    assert!(Foo != Bar);

    assert_eq!(Bar, Bar);

    assert_eq!(Baz, Baz);

    assert_eq!(Foo, Fu);
    assert_eq!(Fu, Foo);
}