如何在循环中返回借用的引用

Question

我有一个带有方法

fn maybe_getv(&mut self) -> Option<&mut i32>

的结构。现在我想实现另一个名为“getv_with_retry”的函数，它在循环中不断重试并返回成功。

struct S {
    v: i32,
}

impl S {
    pub fn maybe_getv(&mut self) -> Option<&mut i32> {
        unimplemented!();  // return Some(&mut self.v) in some cases
    }
}

fn getv_with_retry(s: &mut S) -> Option<&mut i32> {
    loop {
        let result = s.maybe_getv();
        if result.is_some() {
            return result;
        }
    }
}

（链接到 Rust 游乐场：https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=f6ca3e7d0a6c29a0e9d9cdcf902c7ad3）

编译器会报如下错误：

error[E0499]: cannot borrow `*s` as mutable more than once at a time
  --> src/lib.rs:13:22
   |
11 | fn getv_with_retry(s: &mut S) -> Option<&mut i32> {
   |                       - let's call the lifetime of this reference `'1`
12 |     loop {
13 |         let result = s.maybe_getv();
   |                      ^^^^^^^^^^^^^^ `*s` was mutably borrowed here in the previous iteration of the loop
14 |         if result.is_some() {
15 |             return result;
   |                    ------ returning this value requires that `*s` is borrowed for `'1`

我应该如何正确实施

getv_with_retry

？