IMP的原始特征和参考

发布于 2025-02-03 15:02:13 字数 634 浏览 4 评论 0 原文

也许这是一个简单的问题，但是我不明白为什么要对原始的，拥有类型的类型提示特征，我免费获得了参考类型的同一含义...

trait Cool: Sized + std::fmt::Debug {
    fn cool(self) {
        println!("cool -> {:?}", self);
    }
}

impl Cool for i32 {}

// it still works if this line is uncommented...
// impl Cool for &i32 {}

fn main(){
    let val = 123;
    val.cool();
    (&val).cool();
}

playground

原文

Perhaps it is a simple question, but I can't understand why just impl'ing Trait for the primitive, owned type, I got for free the same impl for reference types...

trait Cool: Sized + std::fmt::Debug {
    fn cool(self) {
        println!("cool -> {:?}", self);
    }
}

impl Cool for i32 {}

// it still works if this line is uncommented...
// impl Cool for &i32 {}

fn main(){
    let val = 123;
    val.cool();
    (&val).cool();
}

Playground

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猫七 2025-02-10 15:02:13

不仅是因为原始人，它将适用于实现 复制 。否则就不会工作：

trait Cool: Sized + std::fmt::Debug {
    fn cool(self) {
        println!("cool -> {:?}", self);
    }
}

#[derive(Debug)]
struct NonCopy;

impl Cool for i32 {}
impl Cool for NonCopy {}

fn main(){
    let val = 123;
    val.cool();
    (&val).cool();
    
    let nc = NonCopy{};
    nc.cool();
    (&nc).cool();
}

使用明确的错误代码失败：

error[E0507]: cannot move out of a shared reference
  --> src/main.rs:20:5
   |
20 |     (&nc).cool();
   |     ^^^^^^------
   |     |     |
   |     |     value moved due to this method call
   |     move occurs because value has type `NonCopy`, which does not implement the `Copy` trait
   |

Playground

发生的事情是，使用副本类型，Rust在需要时为您透明地创建了副本。

请注意，即使我们评论上一行 // nc.cool（）; ，它也会失败，这显然会移动值...

It is not just because of primitives, it will work for all types that implement Copy. Will not work otherwise:

trait Cool: Sized + std::fmt::Debug {
    fn cool(self) {
        println!("cool -> {:?}", self);
    }
}

#[derive(Debug)]
struct NonCopy;

impl Cool for i32 {}
impl Cool for NonCopy {}

fn main(){
    let val = 123;
    val.cool();
    (&val).cool();
    
    let nc = NonCopy{};
    nc.cool();
    (&nc).cool();
}

Fails with a clear error code:

error[E0507]: cannot move out of a shared reference
  --> src/main.rs:20:5
   |
20 |     (&nc).cool();
   |     ^^^^^^------
   |     |     |
   |     |     value moved due to this method call
   |     move occurs because value has type `NonCopy`, which does not implement the `Copy` trait
   |

Playground

What it's happening is that with the Copy types rust creates a copy transparently for you when needed.

Note that it fails even if we comment out the previous line // nc.cool();, which obviously moves the value...

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