在内部结构上实现的 Deref 特性中 &self 指的是什么？

Question

我在 reddit post 上找到了这段代码，这让我很困惑。

//We'll recurse all we want, thank you very much!
#![allow(unconditional_recursion)]

use std::ops::Deref;

#[derive(Debug)]
struct Outer<T: Deref<Target = Outer<T>>> {
    inner: T,
}

impl<T: Deref<Target = Outer<T>>> Deref for Outer<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.inner
    }
}

#[derive(Debug)]
struct Inner {}

impl Deref for Inner {
    type Target = Outer<Inner>;

    fn deref(&self) -> &Self::Target {
        //Look at which struct we're implementing Deref for,
        //and then read the next line very carefully.
        &self.inner
    }
}

const I: Inner = Inner {};
const O: Outer<Inner> = Outer { inner: I };

fn main() {
    println!("{:?}", O.inner);
    //Could just keep adding asterisks forever!
    println!("{:?}", *O.inner);
    println!("{:?}", **O.inner);
    println!("{:?}", ***O.inner);

    println!("{:?}", O);
    //Could just keep adding asterisks forever!
    println!("{:?}", *O);
    println!("{:?}", **O);
    println!("{:?}", ***O);
}

具体在这里：

impl Deref for Inner {
    type Target = Outer<Inner>;

    fn deref(&self) -> &Self::Target {
        //Look at which struct we're implementing Deref for,
        //and then read the next line very carefully.
        &self.inner
    }
}

函数return如何引用属于另一个结构的字段？ &self 在这里实际上指的是 Outer 吗？

（此代码每次都因堆栈溢出而崩溃）

Answer 1

确实 Inner 上没有 inner。但在放弃之前，编译器会想，“等等，Inner 是否有一些 Deref 实现？”答案当然是有！我们正在写它！那么，它 return 是什么意思？ Outer<Inner>？好吧，尝试取消引用并在 Outer<Inner> 上找到 inner！也就是说，&self.inner 被转换为 &<Self as Deref>::deref(&self).inner。那就是在行动。

当然，因为我们已经在 <Inner as Deref>::deref() 中，我们再次调用它，递归地......一次又一次......直到我们炸毁堆栈。如果您要删除顶部的 #[allow(unconditional_recursion)]，编译器会警告您 (playground):

warning: function cannot return without recursing
  --> src/main.rs:22:5
   |
22 |     fn deref(&self) -> &Self::Target {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
...
25 |         &self.inner
   |          ---------- recursive call site
   |
   = note: `#[warn(unconditional_recursion)]` on by default
   = help: a `loop` may express intention better if this is on purpose

但是当你说 #[allow(unconditional_recursion)] 时，你告诉编译器“相信我，我知道我在做什么”所以它只是耸耸肩并继续。

在内部结构上实现的 Deref 特性中 &self 指的是什么？

What does &self refer to in the Deref trait implemented on the Inner struct?

rust