arrays - 如何将可变数组划分为可变子数组

Question

我需要将可变数组分成 3 个具有可变元素的可变子数组。

#[derive(Debug)]
struct Server {
    time: i64
}


impl Server {
    fn new(x: i64) -> Server {
        return Server {
            time: x
        }
    } 
}

fn main() {
      let mut arr = Vec::<Server>::new();
      arr.push(Server::new(10));
      arr.push(Server::new(20));
      arr.push(Server::new(30));
      arr.push(Server::new(40));
      arr.push(Server::new(50));

      let mut arr1 = arr.iter_mut().filter(|x| x.time > 20).collect::<Vec<&mut Server>>();
      let mut arr2 = arr.iter_mut().filter(|x| x.time < 20).collect::<Vec<&mut Server>>();
      let mut arr3 = arr.iter_mut().filter(|x| x.time == 20).collect::<Vec<&mut Server>>();
}

接下来，对每个子数组执行不影响主数组的不同操作。 (例如，首先在不影响主数组顺序的情况下对每个子数组进行排序。下一步是在每个子数组上操作其元素。这些更改应反射(reflect)在主数组的元素中)。

目前Rust在编译时对数组进行分割，报如下错误:

error[E0499]: cannot borrow `arr` as mutable more than once at a time
  --> src/main.rs:26:18
   |
25 |   let mut arr1 = arr.iter_mut().filter(|x| x.time > 20).collect::<Vec<&mut Server>>();
   |                  --- first mutable borrow occurs here
26 |   let mut arr2 = arr.iter_mut().filter(|x| x.time < 20).collect::<Vec<&mut Server>>();
   |                  ^^^ second mutable borrow occurs here
 ...
29 | }
   | - first borrow ends here
error[E0499]: cannot borrow `arr` as mutable more than once at a time
  --> src/main.rs:27:18
   |
25 |   let mut arr1 = arr.iter_mut().filter(|x| x.time > 20).collect::<Vec<&mut Server>>();
   |                  --- first mutable borrow occurs here
26 |   let mut arr2 = arr.iter_mut().filter(|x| x.time < 20).collect::<Vec<&mut Server>>();
27 |   let mut arr3 = arr.iter_mut().filter(|x| x.time == 20).collect::<Vec<&mut Server>>();
   |                  ^^^ second mutable borrow occurs here
28 |   
29 | }
   | - first borrow ends here

Answer 1

您可以使用 Iterator::partition将您的 vec 分成两个不同的 vec 而无需克隆内部元素。因为你想要三个不同的拆分，所以你必须使用 partition 两次(顺序无关紧要)。

const THRESHOLD: i64 = 20;

let mut arr = Vec::<Server>::new();
arr.push(Server::new(10));
arr.push(Server::new(20));
arr.push(Server::new(30));
arr.push(Server::new(40));
arr.push(Server::new(50));

let (greater, rest): (Vec<_>, Vec<_>) = arr.into_iter().partition(|s| s.time > THRESHOLD);
let (equal, less): (Vec<_>, Vec<_>) = rest.into_iter().partition(|s| s.time == THRESHOLD);

( playground )

因为 Vectors greater、equal 和 less 拥有相应的元素，所以您可以对它们进行可变访问。