使用静态函数为 trait 实现 trait [英] Implement trait for trait with static function

问题描述

trait Trait<T> {
    fn equality() -> bool;
}

impl<T> PartialEq for Trait<T> {
    fn eq(&self, other: &Trait<T>) -> bool {
        self.equality()
    }
}

结果

main.rs:5:23: 5:31 error: the trait `Trait` cannot be made into an object [E0372]
main.rs:5 impl<T> PartialEq for Trait<T> {

删除静态方法使其可编译.带有 &self 参数的方法也可以编译.

Removing the static method makes it compilable. Methods with &self parameter compile, too.

推荐答案

归结为一个称为对象安全的问题，您可以在 RFC 255;Huon 也在他的博客中很好地解释了对象安全.

It comes down to a matter known as object safety, which you can find information of in RFC 255; Huon has a good explanation of object safety in his blog, too.

基本上，创建一个 trait 对象需要为它自己的 trait 对象隐式定义 trait；在这种情况下，这将是 impl<'a, T>性状 <T>对于 Trait <T>+ 'a.如果可以为所有方法编写有意义的定义，那么特征就是对象安全的.静态方法在这种情况下没有意义——fnquality() ->bool 是，没有 Self 类型来调用 equality 方法?它需要凭空提取一个布尔值，但它恭敬地拒绝这样做.

Basically, making a trait object requires an implied definition of the trait for its own trait object; in this case, that would be impl<'a, T> Trait<T> for Trait<T> + 'a. If it is possible to write meaningful definitions of all the methods, then a trait is object safe. Static methods don’t make sense in this context—what would the body of fn equality() -> bool be, with no Self type around to call the equality method on? It would need to pull a boolean out of thin air, which it respectfully declines to do.

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