Use generic trait parameters to minimize associated types #493
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| /// The mask type returned by each comparison. | ||
| type Mask; | ||
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| pub trait SimdPartialEq<T, const N: usize> |
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imo N should be an associated #[type_const] but last I knew that's not done being implemented yet.
something like:
pub trait SimdLen {
#[type_const]
const LEN: usize;
}
impl<T: SimdElement, const N: usize> SimdLen for Simd<T, N> {
#[type_const]
const LEN: usize = N;
}
impl<T: MaskElement, const N: usize> SimdLen for Mask<T, N> {
#[type_const]
const LEN: usize = N;
}
pub trait SimdBase: SimdLen {
type Element: SimdElement;
}
impl<T: SimdElement, const N: usize> SimdBase for Simd<T, N> {
type Element = T;
}
pub trait SimdPartialEq: SimdBase {
fn simd_eq(self, other: Self) -> Mask<<Self::Element as SimdElement>::Mask, { Self::LEN }>;
...
}
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that would allow your example function's bounds to just be:
fn foo<T: SimdElement>(x: Simd<T, 4>) -> Mask<T::Mask, 4>
where
// output types are completely deduced from the blanket
// SimdBase and SimdLen impls so no additional bounds are needed
Simd<T, 4>: SimdFloat,
{
x.is_sign_negative()
}
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sadly, it seems that hits the bug where specifying bounds hides information that could be deduced so the bound ends up having to be:
Simd<T, 4>: SimdFloat<Element = T, LEN = 4>
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I got it to work with just Simd<T, 4>: SimdFloat by removing SimdFloat: SimdBase and instead having where Self: SimdBase on all items in the trait.
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This improves type inference by removing most associated types. For example, the following function doesn't actually work:
You actually need the constraint
Simd<T, 4>: SimdFloat<Mask = Mask<T::Mask, 4>>.With this PR, the function should look a little more like:
There are still a few instances that need associated types, but we can explore those individually to see if there's a better API.
Also, note that we now end up with a lot of instances of
Mask<<T as SimdElement>::Mask, N>. We can either remove theSimdElement::Maskassociated type with #483 or we can provide an alias to avoid writing that out.