rust - 如何有条件地在结构的两个字段之间进行选择，然后更新所选字段？

Question

我在一个较大的结构中有两个相同类型的结构。我将选择其中一个结构并使用相同的代码执行更新。

简化版:

#[derive(Debug)]
struct Counts {
    value: u16,
    count: u8,
}

#[derive(Debug)]
struct Partitioned {
    even: Counts,
    odd: Counts,
}

fn sort() -> Partitioned {
    let mut even = Counts { value: 2, count: 0 };

    let mut odd = Counts { value: 3, count: 0 };

    for i in 1..30 {
        let mut s = if i % 2 == 0 { even } else { odd };
        s.count = s.count + 1;
        // ... a lot of other code
    }

    Partitioned { even, odd }
}

fn main() {
    println!("{:?}", sort());
}

这不包含关于所有权的投诉:

error[E0382]: use of moved value: `even`
  --> src/main.rs:19:37
   |
19 |         let mut s = if i % 2 == 0 { even } else { odd };
   |                                     ^^^^ value moved here in previous iteration of loop
   |
   = note: move occurs because `even` has type `Counts`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `odd`
  --> src/main.rs:19:51
   |
19 |         let mut s = if i % 2 == 0 { even } else { odd };
   |                                                   ^^^ value moved here in previous iteration of loop
   |
   = note: move occurs because `odd` has type `Counts`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `even`
  --> src/main.rs:24:19
   |
19 |         let mut s = if i % 2 == 0 { even } else { odd };
   |                                     ---- value moved here
...
24 |     Partitioned { even, odd }
   |                   ^^^^ value used here after move
   |
   = note: move occurs because `even` has type `Counts`, which does not implement the `Copy` trait

error[E0382]: use of moved value: `odd`
  --> src/main.rs:24:25
   |
19 |         let mut s = if i % 2 == 0 { even } else { odd };
   |                                                   --- value moved here
...
24 |     Partitioned { even, odd }
   |                         ^^^ value used here after move
   |
   = note: move occurs because `odd` has type `Counts`, which does not implement the `Copy` trait

这是怎么回事？如何在不将所有更新代码复制到 if 的两个 block 的情况下实现它？

Answer 1

取a mutable reference到现场:

let mut s = if i % 2 == 0 { &mut even } else { &mut odd };