问题描述
我试图专门化一个特征,但由于实现冲突"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:
I tried to specialize a trait, and it fails to compile because of "conflicting implementations". But my understanding of specialization is that more specific implementations should override more generic ones. Here is a very basic example:
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>`
我原以为具有 &'static str
实际类型的更具体的淹没实现将允许专门的实现,但它无法编译.
I would have expected that the more specific drowning implementation with an actual type of &'static str
would allow specialized implementation, but instead it fails to compile.
推荐答案
专业化尚未稳定.您需要使用 Rust 每晚构建并通过在第一行添加 #![feature(specialization)]
来启用专业化.
Specialization is not yet stabilized. You need to use nightly build of Rust and enable specialization by adding #![feature(specialization)]
in the first line.
然后您需要修复代码中的两个小错误(私有 inner
字段和缺少 use living::Swimmer;
),但这很简单.
Then you'll need to fix two minor errors in your code (private inner
field and lack of use swimming::Swimmer;
), but that is straightforward.
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