如何解决错误 ‘already mutably borrowed: BorrowError’

huangapple
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英文:

how to solve the error 'already mutably borrowed: BorrowError'

问题

我不太擅长处理Rust中的RefCell，我想知道如何解决以下错误。

如果有人能回答我的问题，我将非常感激。

thread 'main' panicked at 'already mutably borrowed: BorrowError', src/main.rs:47:22

rust playground

英文:

I'm not very skilled with rust RefCell

and i want to know how to solve the following error.

I would be very grateful if someone could answer my question.

thread 'main' panicked at 'already mutably borrowed: BorrowError', src/main.rs:47:22

  1. use std::{
  2.     cell::RefCell,
  3.     rc::{Rc, Weak},
  4. };
  6. // parent
  7. struct P {
  8.     i: Rc<RefCell<I>>,
  9. }
  11. impl P {
  12.     fn new() -> P {
  13.         let b = B {
  14.             v: "b".to_string(),
  15.             i: Weak::new(),
  16.         };
  17.         let c = C {
  18.             v: "c".to_string(),
  19.             i: Weak::new(),
  20.         };
  21.         let i = Rc::new(RefCell::new(I { b, c }));
  22.         let ii = i.clone();
  23.         let p = P { i };
  25.         // init b.i
  26.         let mut borrow_mut = RefCell::borrow_mut(&ii);
  27.         let bb = &mut borrow_mut.b;
  28.         bb.i = Rc::downgrade(&ii);
  30.         // init c.i
  31.         let cc = &mut borrow_mut.c;
  32.         cc.i = Rc::downgrade(&ii);
  33.         p
  34.     }
  36.     fn update_bv_cv(&self) {
  37.         // update b.v
  38.         let mut borrow_mut = RefCell::borrow_mut(&self.i);
  39.         let b = &mut borrow_mut.b;
  40.         b.v.push_str("=>p.update_bv_cv");
  42.         // update c.v
  43.         let c = &mut borrow_mut.c;
  44.         c.v.push_str("=>p.update_bv_cv");
  46.         // b update c.v
  47.         let borrow = RefCell::borrow(&self.i);
  48.         let b = &borrow.b;
  49.         b.update_cv();
  50.     }
  52.     fn get_bv_cv(&self) -> (String, String) {
  53.         let i = &self.i;
  54.         let ii = i.borrow();
  56.         let bv = ii.b.v.as_str();
  57.         let cv = ii.c.v.as_str();
  59.         (bv.into(), cv.into())
  60.     }
  61. }
  63. // parent inner
  64. struct I {
  65.     c: C,
  66.     b: B,
  67. }
  69. // child
  70. struct C {
  71.     i: Weak<RefCell<I>>,
  72.     v: String,
  73. }
  75. // child
  76. struct B {
  77.     i: Weak<RefCell<I>>,
  78.     v: String,
  79. }
  81. impl B {
  82.     fn update_cv(&self) {
  83.         if let Some(i) = self.i.upgrade() {
  84.             let mut ii = RefCell::borrow_mut(&i);
  85.             ii.c.v.push_str("b.udpate_cv");
  86.         }
  87.     }
  88. }
  90. fn main() {
  91.     let p = P::new();
  92.     p.update_bv_cv();
  93.     let (bv, cv) = p.get_bv_cv();
  94.     println!("b.v: {bv}\nc.v: {cv}");
  95. }

rust playground

答案1

得分: 2

来自URLO的交叉帖子

以下是一个安全的解决方案：

  1. let i = {
  2.     // b更新c.v
  3.     let ref_i = RefCell::borrow(&self.i); // RefCell::<I>::borrow::<'r>(&'r self) -> Ref<'r, I>
  4.     ref_i.b.i.clone() // 通过克隆Weak来丢弃 'r
  5. };
  6. update_cv_from_b(&i);
  8. fn update_cv_from_b(i: &Weak<RefCell<I>>) {
  9.     if let Some(i) = i.upgrade() {
  10.         let mut ii = RefCell::borrow_mut(&i);
  11.         ii.c.v.push_str("b.udpate_cv");
  12.     }
  13. }

playground

英文:

Came from a cross post in URLO

And here's a safe solution:

  1. let i = {
  2.     // b update c.v
  3.     let ref_i = RefCell::borrow(&amp;self.i); // RefCell::&lt;I&gt;::borrow::&lt;&#39;r&gt;(&amp;&#39;r self) -&gt; Ref&lt;&#39;r, I&gt;
  4.     ref_i.b.i.clone() // throw away &#39;r via cloning Weak
  5. };
  6. update_cv_from_b(&amp;i);
  8. fn update_cv_from_b(i: &amp;Weak&lt;RefCell&lt;I&gt;&gt;) {
  9.     if let Some(i) = i.upgrade() {
  10.         let mut ii = RefCell::borrow_mut(&amp;i);
  11.         ii.c.v.push_str(&quot;b.udpate_cv&quot;);
  12.     }
  13. }

playground

huangapple
  • 本文由 发表于 2023年2月27日 08:28:13
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  • refcell
  • rust
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