如何获取对 RwLock 中对象的引用?

How to get a reference to the object inside an RwLock?

此代码有效:

use serde::{Deserialize, Serialize};
use std::sync::{RwLock, Arc};
use ron;

#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq, PartialOrd, Ord)]
struct Foo {
    first: u8,
    second: u16,
}

fn main() {
    let foo = Foo {first: 1, second: 2};
    let lock = Arc::new(RwLock::new(foo));

    let state = lock.read().unwrap().clone(); // FIXME: remove clone()
    let string = ron::ser::to_string(&state).unwrap();
    println!("{}", string);
}

我想去掉.clone(),因为我程序中的foo是100MB+,我需要多次引用这个引用。

当我摆脱 .clone() 时,我得到错误:

error[E0277]: the trait bound `std::sync::RwLockReadGuard<'_, Foo>: _::_serde::Serialize` is not satisfied
  --> src/bin/sandbox7.rs:16:35
   |
16 |     let string = ron::ser::to_string(&state).unwrap();
   |                                      ^^^^^^ the trait `_::_serde::Serialize` is not implemented for `std::sync::RwLockReadGuard<'_, Foo>`
   | 
  ::: /home/chris/.cargo/registry/src/github.com-1ecc6299db9ec823/ron-0.6.0/src/ser/mod.rs:25:8
   |
25 |     T: Serialize,
   |        --------- required by this bound in `ron::ser::to_string`

我想序列化 foo(来自另一个线程,在真实代码中,因此是 Arc)。

我怎样才能从 lock 得到 &Foo,而不浪费 .clone()

RWLockReadGuard derefs 到基础类型。

操场上没有 ron,所以我无法确定,但这应该可以解决问题:

let state = lock.read().unwrap();
let string = ron::ser::to_string(&*state).unwrap();