Function keys

cranelift/entity/src/primary.rs:472–482

()

    }
    #[test]
    fn keys() {
        let mut m: PrimaryMap<E, usize> = PrimaryMap::new();
        m.push(12);
        m.push(33);

        let mut i = 0;
        for key in m.keys() {
            assert_eq!(key.index(), i);
            i += 1;
        }
    }

    #[test]
    fn keys_rev() {