Rust 以 `static` 为前缀的闭包是什么意思我什么时候使用它

我偶然发现了一个在文档中有static || { }个有效的例子.然而，在我自己的代码中使用这种表达式的try 失败了.我想知道为什么.

来自https://doc.rust-lang.org/stable/std/pin/macro.pin.html个人的例子

#![feature(generators, generator_trait)]
use std::{
    ops::{Generator, GeneratorState},
    pin::pin,
};

fn generator_fn() -> impl Generator<Yield = usize, Return = ()> /* not Unpin */ {
 // Allow generator to be self-referential (not `Unpin`)
 // vvvvvv        so that locals can cross yield points.
    static || {
        let foo = String::from("foo");
        let foo_ref = &foo; // ------+
        yield 0;                  // | <- crosses yield point!
        println!("{foo_ref}"); // <--+
        yield foo.len();
    }
}

fn main() {
    let mut generator = pin!(generator_fn());
    match generator.as_mut().resume(()) {
        GeneratorState::Yielded(0) => {},
        _ => unreachable!(),
    }
    match generator.as_mut().resume(()) {
        GeneratorState::Yielded(3) => {},
        _ => unreachable!(),
    }
    match generator.resume(()) {
        GeneratorState::Yielded(_) => unreachable!(),
        GeneratorState::Complete(()) => {},
    }
}

我的try 失败了:

fn func() -> impl Fn() {
    static || {
        println!("qwerty");
    }
}

出现以下错误:

error[E0697]: closures cannot be static
 --> ./ex_099.rs:2:5
  |
2 |     static || {
  |     ^^^^^^^^^

铁 rust 版本:

$ rustc --version
rustc 1.70.0-nightly (88fb1b922 2023-04-10)