Marker types should implement standard traits (Hash, Eq, etc.)

[zwarich]

It was surprising to me that the program

use std::kinds::marker::ContravariantLifetime;

#[deriving(Hash, Eq, PartialEq)]
struct A<'a> {
    x: u64,
    marker: ContravariantLifetime<'a>,
}

fn main() { }

gives this error:

test.rs:6:5: 6:38 error: type `core::kinds::marker::ContravariantLifetime<'_>` does not implement any method in scope named `assert_receiver_is_total_eq`
test.rs:6     marker: ContravariantLifetime<'a>,
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.rs:3:18: 3:20 note: in expansion of #[deriving(Eq)]
test.rs:6:5: 6:38 note: expansion site
test.rs:6:5: 6:38 error: type `core::kinds::marker::ContravariantLifetime<'_>` does not implement any method in scope named `hash`
test.rs:6     marker: ContravariantLifetime<'a>,
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.rs:3:12: 3:16 note: in expansion of #[deriving(Hash)]
test.rs:6:5: 6:38 note: expansion site
error: aborting due to 2 previous errors

[nham]

I think the updated equivalent of this code is:

use std::marker::PhantomData;

#[derive(Hash, Eq, PartialEq)]
struct A<'a> {
    x: u64,
    marker: PhantomData<&'a ()>,
}

fn main() { }

which compiles on this version of rust-nightly:

rustc 1.0.0-nightly (a52182ffd 2015-04-17) (built 2015-04-17)

So it seems this issue may be resolved.

[alexcrichton]

Thanks @nham!