我正在尝试设计一对特征(例如来自线性代数的RowVector
和ColumnVector
),其中每个特征从其中一个方法返回另一个特征(例如transpose
)。我希望将来能够添加任何特征的实现(例如密集和稀疏矢量实现)。
#[macro_use]
extern crate derive_new;
trait RowVector<Element> {
fn transpose(self) -> ColumnVector<Element>;
}
trait ColumnVector<Element> {
fn transpose(self) -> RowVector<Element>;
}
#[derive(new, Debug)]
struct VecRowVector<Element> {
vec: Vec<Element>
}
#[derive(new, Debug)]
struct VecColumnVector<Element> {
vec: Vec<Element>
}
impl<Element> RowVector<Element> for VecRowVector<Element> {
fn transpose(self) -> VecColumnVector<Element> {
VecColumnVector::new(self.vec)
}
}
impl<Element> ColumnVector<Element> for VecColumnVector<Element> {
fn transpose(self) -> VecRowVector<Element> {
VecRowVector::new(self.vec)
}
}
fn main() {
let row_vector = VecRowVector::new(vec![1,2,3]);
let col_vector = VecColumnVector::new(vec![1,2,3]);
println!("{:?}", row_vector.transpose());
println!("{:?}", col_vector.transpose());
}
我收到一条错误消息,指出VecColumnVector
不是ColumnVector
,并且期望'static
值。
error[E0053]: method `transpose` has an incompatible type for trait
--> src\main.rs:22:31
|
4 | fn transpose(self) -> ColumnVector<Element>;
| --------------------- type in trait
...
22 | fn transpose(self) -> VecColumnVector<Element> {
| ^^^^^^^^^^^^^^^^^^^^^^^^ expected trait ColumnVector, found struct `VecColumnVector`
|
= note: expected type `fn(VecRowVector<Element>) -> ColumnVector<Element> + 'static`
= note: found type `fn(VecRowVector<Element>) -> VecColumnVector<Element>`
我没有VecColumnVector
ColumnVector
的子类型吗?或者我是否需要告诉特性它不需要static
一生?
答案 0 :(得分:2)
您正在尝试返回特征。虽然使用trait object可以实现这一点,但这可能不是您想要做的。更好的设计是引入Transpose
特征,您可以使用与Rust的内置From
和Into
转换特征类似的方式进行建模。
trait Transpose<To> {
fn transpose(self) -> To;
}
impl<Element> Transpose<VecColumnVector<Element>> for VecRowVector<Element> {
fn transpose(self) -> VecColumnVector<Element> {
VecColumnVector::new(self.vec)
}
}
impl<Element> Transpose<VecRowVector<Element>> for VecColumnVector<Element> {
fn transpose(self) -> VecRowVector<Element> {
VecRowVector::new(self.vec)
}
}
答案 1 :(得分:1)
当需要关联两种类型时,最佳解决方案通常为associated types。这排除了使用像特征对象一样的动态调度,但在Rust中动态调度仍然非常有限。使用静态调度时,Rust更具表现力,相关类型具有杠杆作用。
pub trait RowVector<Element>: Sized {
type Transpose: ColumnVector<Element>;
fn transpose(self) -> Self::Transpose;
}
pub trait ColumnVector<Element>: Sized {
type Transpose: RowVector<Element>;
fn transpose(self) -> Self::Transpose;
}
pub struct VecRowVector<Element> {
pub vec: Vec<Element>
}
pub struct VecColumnVector<Element> {
pub vec: Vec<Element>
}
impl<Element> RowVector<Element> for VecRowVector<Element> {
type Transpose = VecColumnVector<Element>;
fn transpose(self) -> VecColumnVector<Element> {
VecColumnVector { vec: self.vec }
}
}
impl<E: Debug> ColumnVector<Element> for VecColumnVector<Element> {
type Transpose = VecRowVector<Element>;
fn transpose(self) -> VecRowVector<Element> {
VecRowVector { vec: self.vec }
}
}