[英]How does trait specialization actually work?
我試圖專門研究一個特性,由於“沖突的實現”而無法編譯。 但是我對專業化的理解是,更具體的實現應優先於更通用的實現。 這是一個非常基本的示例:
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()
}
錯誤是:
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>`
我本來希望具有實際類型的&'static str
的更具體的溺水實現將允許專門的實現,但是相反,它無法編譯。
專業化尚未穩定。 您需要使用Rust的每晚構建,並通過在第一行中添加#![feature(specialization)]
來啟用專業化。
然后,您需要修復代碼中的兩個小錯誤(私有inner
字段和缺少use swimming::Swimmer;
),但這很簡單。
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