特质专业化如何实际起作用？

Question

我试图专门化一个特性,但由于"实施冲突"而无法编译.但我对专业化的理解是,更具体的实现应该覆盖更通用的实现.这是一个非常基本的例子:

mod diving {
    pub struct Diver<T> {
        inner: T
    }
}

mod swimming {
    use diving;
    pub trait Swimmer {
        fn swim(&self) {
            println!("swimming")
        }
    }

    impl<T> Swimmer for diving::Diver<T> {

    }
}

mod drowning {
    use diving;
    use swimming;
    impl swimming::Swimmer for diving::Diver<&'static str> {
        fn swim(&self) {
            println!("drowning, help!")
        }
    }
}

fn main() {
    let x = diving::Diver::<&'static str> {
        inner: "Bob"
    };
    x.swim()
}

错误是:

rustc 1.18.0 (03fc9d622 2017-06-06)
error[E0119]: conflicting implementations of trait `swimming::Swimmer` for type `diving::Diver<&'static str>`:
  --> <anon>:23:5
   |
15 | /     impl<T> Swimmer for diving::Diver<T> {
16 | |     
17 | |     }
   | |_____- first implementation here
...
23 | /     impl swimming::Swimmer for diving::Diver<&'static str> {
24 | |         fn swim(&self) {
25 | |             println!("drowning, help!")
26 | |         }
27 | |     }
   | |_____^ conflicting implementation for `diving::Diver<&'static str>`

我原本期望具有实际类型的更具体的淹没实现&'static str将允许专门的实现,但是它无法编译.

Answer 1

专业化尚未稳定.您需要使用每晚构建的Rust并通过添加#![feature(specialization)]第一行来启用特化.

然后你需要修复代码中的两个小错误(私有inner字段和缺少use swimming::Swimmer;),但这很简单.

最终代码