Cannot have the same supertrait twice, but with different type parameters

[burtonageo]

I am writing a Euclidean Vector class, and want to override some operations for it. However, when I try to add mul for both Vector-Vector multiplication and Vector-Scalar multiplication, the compiler complains that there is a Duplicate supertrait in trait declaration:

euclidean_vector.rs:5:0: 20:1 error: Duplicate supertrait in trait declaration
euclidean_vector.rs:5 pub trait EuclideanVector<T: Num + Algebraic> : 
euclidean_vector.rs:6   Add<Self, Self> +
euclidean_vector.rs:7   Sub<Self, Self> +
euclidean_vector.rs:8   Mul<Self, Self> +
euclidean_vector.rs:9   Mul<T, Self> +
euclidean_vector.rs:10   One + Zero +

[emberian]

cc @nikomatsakis, does your current work also include this?

[nikomatsakis]

On Mon, Apr 07, 2014 at 10:42:04AM -0700, Corey Richardson wrote:

cc @nikomatsakis, does your current work also include this?

Yes.

Closing, this is now supported.

[nikomatsakis]

Actually that's not true. That portion of the work never landed.

[nikomatsakis]

e.g. this example still fails to compile:

trait Foo<T> { }

trait Bar : Foo<int> + Foo<uint> { }

fn main() { }

I think there are some subtle issues here that would have to be addressed eventually, particularly around object types.

[nikomatsakis]

I've wound up fixing this kind of by accident as part of another patch.