rust - 如何在Abs中实现Abs函数以自定义类型？

Question

我目前正在使用Rust编写数字代码。所以我自己为它创建了一个类型。
此特征是允许rust_ndarray在f64和f32上执行计算的数据方式。为了使其具有多线程，我们在特征的边界添加了“同步”和“发送”。
如何在其他整数类型中找到的我自己的类型中实现函数？

use ndarray_linalg::lapack::Lapack;
use ndarray_linalg::types::Scalar;
use ndarray_linalg::rand_distr::Float;
use std::marker::{Sync, Send};

pub trait Type: Lapack + Scalar + Float + Sync + Send {}

impl Type for f32 {}
impl Type for f64 {}

我想编写自己的函数来查找此Type的绝对值。
我该如何实现？
我做了如下所示的实现，并收到以下错误。

impl Type {
    pub fn abs(&self) -> Self {
        if self.0 > 0. {self.0}
        else {-1. * self.0}
    }
}

我收到以下错误。
鉴于我收到的错误，我在Type中使用的特征边界似乎有问题。我还尝试在trate边界中包括ParticalOrd和ParticalEq并收到相同的错误。

note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
    |
   ::: src/traits.rs:7:11
    |
7   | pub trait Type: Lapack + Scalar + Float + Sync + Send {}
    |           ------- this trait cannot be made into an object...
   --> /Users/~~/.cargo/registry/src/github.com-1ecc6299db9ec823/rand_distr-0.2.2/src/utils.rs:24:33
    |
24  | pub trait Float: Copy + Sized + cmp::PartialOrd
    |                                 ^^^^^^^^^^^^^^^ ...because it uses `Self` as a type parameter
25  |     + ops::Neg<Output = Self>
26  |     + ops::Add<Output = Self>
    |       ^^^^^^^^^^^^^^^^^^^^^^^
    |       |        |
    |       |        ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
27  |     + ops::Sub<Output = Self>
    |       ^^^^^^^^^^^^^^^^^^^^^^^
    |       |        |
    |       |        ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
28  |     + ops::Mul<Output = Self>
    |       ^^^^^^^^^^^^^^^^^^^^^^^
    |       |        |
    |       |        ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
29  |     + ops::Div<Output = Self>
    |       ^^^^^^^^^^^^^^^^^^^^^^^
    |       |        |
    |       |        ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
30  |     + ops::AddAssign + ops::SubAssign + ops::MulAssign + ops::DivAssign
    |       ^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^ ...because it uses `Self` as a type parameter
    |       |                |                |
    |       |                |                ...because it uses `Self` as a type parameter
    |       |                ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
    |
   ::: /Users/~~/.cargo/registry/src/github.com-1ecc6299db9ec823/cauchy-0.2.2/src/lib.rs:44:7
    |
44  |     + Sum
    |       ^^^ ...because it uses `Self` as a type parameter
45  |     + Product
    |       ^^^^^^^ ...because it uses `Self` as a type parameter
    |
   ::: /Users/~~/.cargo/registry/src/github.com-1ecc6299db9ec823/num-traits-0.2.14/src/lib.rs:67:41
    |
67  | pub trait Num: PartialEq + Zero + One + NumOps {
    |                ^^^^^^^^^                ^^^^^^ ...because it uses `Self` as a type parameter
    |                |
    |                ...because it uses `Self` as a type parameter
...
149 | pub trait NumAssign: Num + NumAssignOps {}
    |                            ^^^^^^^^^^^^ ...because it uses `Self` as a type parameter
    |
   ::: /Users/~~/.cargo/registry/src/github.com-1ecc6299db9ec823/num-traits-0.2.14/src/identities.rs:12:25
    |
12  | pub trait Zero: Sized + Add<Self, Output = Self> {
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^
    |                         |         |
    |                         |         ...because it uses `Self` as a type parameter
    |                         ...because it uses `Self` as a type parameter
...
90  | pub trait One: Sized + Mul<Self, Output = Self> {
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^
    |                        |         |
    |                        |         ...because it uses `Self` as a type parameter
    |                        ...because it uses `Self` as a type parameter

error[E0038]: the trait `Type` cannot be made into an object
   --> src/traits.rs:13:6



13  | impl Type {
    |      ^^^^^^^ `Type` cannot be made into an object
    |
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
    |
   ::: src/traits.rs:7:11
    |
7   | pub trait Type: Lapack + Scalar + Float + Sync + Send {}
    |           ------- this trait cannot be made into an object...
   --> /Users/~~/.cargo/registry/src/github.com-1ecc6299db9ec823/rand_distr-0.2.2/src/utils.rs:24:33
    |
24  | pub trait Float: Copy + Sized + cmp::PartialOrd
    |                                 ^^^^^^^^^^^^^^^ ...because it uses `Self` as a type parameter
25  |     + ops::Neg<Output = Self>
26  |     + ops::Add<Output = Self>
    |       ^^^^^^^^^^^^^^^^^^^^^^^
    |       |        |
    |       |        ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
27  |     + ops::Sub<Output = Self>
    |       ^^^^^^^^^^^^^^^^^^^^^^^
    |       |        |
    |       |        ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
28  |     + ops::Mul<Output = Self>
    |       ^^^^^^^^^^^^^^^^^^^^^^^
    |       |        |
    |       |        ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
29  |     + ops::Div<Output = Self>
    |       ^^^^^^^^^^^^^^^^^^^^^^^
    |       |        |
    |       |        ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
30  |     + ops::AddAssign + ops::SubAssign + ops::MulAssign + ops::DivAssign
    |       ^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^ ...because it uses `Self` as a type parameter
    |       |                |                |
    |       |                |                ...because it uses `Self` as a type parameter
    |       |                ...because it uses `Self` as a type parameter
    |       ...because it uses `Self` as a type parameter
    |
   ::: /Users/~~/.cargo/registry/src/github.com-1ecc6299db9ec823/cauchy-0.2.2/src/lib.rs:44:7
    |
44  |     + Sum
    |       ^^^ ...because it uses `Self` as a type parameter
45  |     + Product
    |       ^^^^^^^ ...because it uses `Self` as a type parameter
    |
   ::: /Users/~~/.cargo/registry/src/github.com-1ecc6299db9ec823/num-traits-0.2.14/src/lib.rs:67:41
    |
67  | pub trait Num: PartialEq + Zero + One + NumOps {
    |                ^^^^^^^^^                ^^^^^^ ...because it uses `Self` as a type parameter
    |                |
    |                ...because it uses `Self` as a type parameter
...
149 | pub trait NumAssign: Num + NumAssignOps {}
    |                            ^^^^^^^^^^^^ ...because it uses `Self` as a type parameter
    |
   ::: /Users/~~/.cargo/registry/src/github.com-1ecc6299db9ec823/num-traits-0.2.14/src/identities.rs:12:25
    |
12  | pub trait Zero: Sized + Add<Self, Output = Self> {
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^
    |                         |         |
    |                         |         ...because it uses `Self` as a type parameter
    |                         ...because it uses `Self` as a type parameter
...
90  | pub trait One: Sized + Mul<Self, Output = Self> {
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^
    |                        |         |
    |                        |         ...because it uses `Self` as a type parameter
    |                        ...because it uses `Self` as a type parameter

Answer 1

您的Type实际上不是数据类型，而是特征。而且，当您为特征编写impl时，实际上是为该特征的dyn对象版本编写的，而这通常不是您想要的。实际上，您可能会收到类似以下的警告:

warning: trait objects without an explicit `dyn` are deprecated

由于您的特征要求不是动态对象安全的，因此会出现其余错误。
您可能需要的是特征中的一个简单函数:

pub trait Type: Lapack + Scalar + Float + Sync + Send {
    fn abs(&self) -> Self;
}
impl Type for f32 {
    fn abs(&self) -> Self {
        Self::abs(*self)
    }
}
impl Type for f64 {
    fn abs(&self) -> Self {
        Self::abs(*self)
    }
}

是的，您必须为实现 Type的每种类型重复该代码，但是在这种情况下，这几乎没有什么不便之处。
如果有很多类型和很多功能，则可以使用宏，这就是大多数库所做的。