rust - 是否可以解构方法的 `self` 参数？

Question

我正在尝试找到一种方法来解构方法的 self 参数。根据GitHub comment :

Per today's meeting, we have a different plan to make self arguments destructurable. With universal function-call syntax (UFCS #11938) there will not be any distinction between static methods and instance methods - they will both be 'associated functions'. At that point any function who's first argument is the self type will be callable with method syntax, and self, &self, and &mut self are just sugar for i.e. self: &Self, and destructuring on the self argument can be done as normal by not using the self-sugar.

我写了下面的代码，但它没有像我预期的那样工作，因为所有三个打印函数都可以用作方法。

struct Vector {
    x: i32,
    y: i32,
    z: i32,
}

impl Vector {
    fn print1(self: &Self) {
        println!("{} {} {}", self.x, self.y, self.z);
    }

    // destructure self argument
    fn print2(&Vector{x, y, z}: &Self) {
        println!("{} {} {}", x, y, z);
    }

    // use another name for the first argument
    fn print3(this: &Self) {
        println!("{} {} {}", this.x, this.y, this.z);
    }
}

fn main() {
    let v = Vector{x: 1, y: 2, z: 3};

    Vector::print1(&v); // work
    v.print1();         // work
    Vector::print2(&v); // work
    v.print2();         // not work
    Vector::print3(&v); // work
    v.print3();         // not work
}

print3() 只是用来测试是否可以使用 self 以外的名称作为方法的第一个参数。

它给出了这个编译错误:

error: no method named `print2` found for type `Vector` in the current scope
  --> 1.rs:27:7
   |
27 |     v.print2();         // not work
   |       ^^^^^^
   |
   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
note: candidate #1 is defined in an impl for the type `Vector`
  --> 1.rs:12:5
   |
12 |       fn print2(&Vector{x, y, z}: &Self) {
   |  _____^ starting here...
13 | |         println!("{} {} {}", x, y, z);
14 | |     }
   | |_____^ ...ending here

error: no method named `print3` found for type `Vector` in the current scope
  --> 1.rs:29:7
   |
29 |     v.print3();         // not work
   |       ^^^^^^
   |
   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
note: candidate #1 is defined in an impl for the type `Vector`
  --> 1.rs:16:5
   |
16 |       fn print3(this: &Self) {
   |  _____^ starting here...
17 | |         println!("{} {} {}", this.x, this.y, this.z);
18 | |     }
   | |_____^ ...ending here

似乎 print2() 和 print3() 没有被识别为 Vector 的方法。

1. 如何解构方法的self参数？
2. 根据评论，self 这个名字只是糖。这是否意味着方法的第一个参数可以使用 self 以外的名称？

Answer 1

这最初是为了实现通用函数调用，但向后不兼容，因为这意味着 fn foo(bar: &Self) 会突然等同于 fn foo (self: &Self)，由于突然出现新方法，可能会中断方法调用。

this github issue comment 中的完整理由

您可以在函数体中使用 let 绑定(bind)来解构显式 self 参数:

let &Vector { x, y, z } = self;