此问题已在此处有答案：

How to write a trait bound for adding two references of a generic type?（1个答案）
15小时前关门了。
下面是我的原始代码，它可以工作：

pub trait Arith {
    fn square(x: &Self) -> Self;
}

impl Arith for i32 {
     fn square(x: &i32) -> i32 {
         x * x
     }
}

impl Arith for f32 {
    fn square(x: &f32) -> f32 {
        x * x
    }
}

我想用一种通用的方式来做：

pub trait Arith where Self: Sized + Mul<&Self, Output = Self> {
    fn square(x: &Self) -> Self {
        x * x
    }
}

似乎我遇到了一些生命周期注解问题：

error[E0637]: `&` without an explicit lifetime name cannot be used here
 --> src/main.rs:7:41
  |
7 | pub trait Arith where Self: Sized + Mul<&Self, Output = Self> {
  |                                         ^ explicit lifetime name needed here
  |
help: consider introducing a higher-ranked lifetime here with `for<'a>`
 --> src/main.rs:7:37
  |
7 | pub trait Arith where Self: Sized + Mul<&Self, Output = Self> {
  |                                     ^

error[E0311]: the parameter type `Self` may not live long enough
 --> src/main.rs:7:37
  |
7 | pub trait Arith where Self: Sized + Mul<&Self, Output = Self> {
  |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the reference type `&Self` does not outlive the data it points at

Some errors have detailed explanations: E0311, E0637.
For more information about an error, try `rustc --explain E0311`.

我尝试了编译器建议的几种方法，但无法使其工作。我更喜欢函数调用看起来像Arith::square(&x)。