为什么在专门化特征时会出现冲突的实现错误?

Question

我不确定我是否理解为什么这段代码无法编译。似乎新的"向量"Mul专业化比默认的更具体，我不认为我依赖于没有为我的板条箱外部类型定义的Vectorizable特征。

#![feature(cfg_target_feature)]
#![feature(specialization)]
use std::marker::PhantomData;
use std::ops::{Mul, Add};
type Dimension = (usize, usize);
type Coordinate = (usize, usize);
pub trait Ordering {
// omitted
}
pub struct RowMajor {}
impl Ordering for RowMajor {}
pub struct ColumnMajor {}
impl Ordering for ColumnMajor {}
// NxM matrix
pub struct Matrix<T, O: Ordering> {
dim: Dimension,
values: Vec<T>,
// needed so that we can add type bound to struct
ordering: PhantomData<O>,
}
trait VectorSize {}
struct V4x {}
impl VectorSize for V4x {}
// others defined for other sizes
trait Vectorizable {
type SimdType; /*: simd::Simd */
type VectorSize: VectorSize;
}
#[cfg(target_feature = "sse")]
impl Vectorizable for f32 {
type SimdType = f32; /* simd::f32x4 */
type VectorSize = V4x;
}
impl<'a, 'b, T1, T2, O1: Ordering, O2: Ordering>
Mul<&'b Matrix<T2, O2>> for &'a Matrix<T1, O1>
where
T1: Mul<T2> + Clone,
T2: Clone,
<T1 as Mul<T2>>::Output: Add<Output = <T1 as Mul<T2>>::Output> + Clone + Default,
{
// always output row major because we compute in row major order
type Output = Matrix<
<T1 as Mul<T2>>::Output
, RowMajor>;
// self is a &'a
default fn mul(self, rhs: &'b Matrix<T2, O2>) -> Self::Output
{
unimplemented!();
}
}
impl<'a, 'b, T: Vectorizable> Mul<&'b Matrix<T, ColumnMajor>> for &'a Matrix<T, RowMajor> {
fn mul(self, rhs: &'b Matrix<T, ColumnMajor>) -> Self::Output {
unimplemented!();
}
}

(游乐场(

error[E0119]: conflicting implementations of trait `std::ops::Mul<&Matrix<_, ColumnMajor>>` for type `&Matrix<_, RowMajor>`:
--> src/main.rs:65:1
|
46 | / impl<'a, 'b, T1, T2, O1: Ordering, O2: Ordering>
47 | |     Mul<&'b Matrix<T2, O2>> for &'a Matrix<T1, O1>
48 | | where
49 | |     T1: Mul<T2> + Clone,
...  |
62 | |     }
63 | | }
| |_- first implementation here
64 | 
65 | / impl<'a, 'b, T: Vectorizable> Mul<&'b Matrix<T, ColumnMajor>> for &'a Matrix<T, RowMajor> {
66 | |     fn mul(self, rhs: &'b Matrix<T, ColumnMajor>) -> Self::Output {
67 | |         unimplemented!();
68 | |     }
69 | | }
| |_^ conflicting implementation for `&Matrix<_, RowMajor>`

Answer 1

Vectorizable实现没有更具体，例如，它没有提到任何关于T * T是一般操作所需的有效操作。

您需要向Vectorizableimpl 添加更多边界以匹配常规边界：

impl<'a, 'b, T> Mul<&'b Matrix<T, ColumnMajor>> for &'a Matrix<T, RowMajor> 
where
T: Vectorizable + Mul + Clone,
T::Output: Add<Output = T::Output> + Clone + Default,
{

或者，您可以将这些边界添加为Vectorizable的超级特征：

trait Vectorizable: Mul<Output=Self> + Add<Output = Self> + Clone + Default {
// ...
}
impl<'a, 'b, T: Vectorizable> Mul<&'b Matrix<T, ColumnMajor>> for &'a Matrix<T, RowMajor> {
// ...
}