arrays - Rust-如何初始化包含HashSet字段的结构数组？

Question

我有带有Instance字段的HashSet结构，用于存储无序数字，并易于删除和添加重复项控件。

然后是另一个名为Matrix的结构，它包含Instance结构的二维数组。

我在trait中创建了new()方法，以便Instance在数组初始化中使用，但是使用此方法会在编译期间出错，并说HashSet没有实现Copy特质。

这是代码:

#![allow(unused)]
use std::collections::HashSet;

struct Instance {
    ids: HashSet<u8>,
    value: u8,
}

trait IsInstance {
    fn new() -> Instance;
}

impl IsInstance for Instance {
    fn new() -> Instance {
        Instance {
            ids: [1, 2, 3, 5].iter().cloned().collect(),
            value: 0,
        }
    }
}

/*
Line below is commented due to error:

error[E0204]: the trait `Copy` may not be implemented for this type
  --> src/main.rs:26:6
   |
5  |     ids: HashSet,
   |     ---------------- this field does not implement `Copy`
...
26 | impl Copy for Instance {}
   |      ^^^^

*/
//impl Copy for Instance {}

impl Clone for Instance {
    fn clone(&self) -> Instance {
        Instance {
            ids: self.ids,
            value: self.value,
        }
    }
}

struct Matrix {
    instances: [[Instance; 4]; 4],
    status: u8,
}

fn main() {
    let mut m = Matrix {
        instances: [[Instance::new(); 4]; 4],
        status: 0,
    };
}

编译此错误:

error[E0507]: cannot move out of `self.ids` which is behind a shared reference
  --> src/main.rs:42:18
   |
42 |             ids: self.ids, 
   |                  ^^^^^^^^ move occurs because `self.ids` has type `std::collections::HashSet<u8>`, which does not implement the `Copy` trait

error[E0277]: the trait bound `Instance: std::marker::Copy` is not satisfied
  --> src/main.rs:60:22
   |
60 |         instances : [[Instance::new(); 4]; 4],
   |                      ^^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `Instance`
   |
   = note: the `Copy` trait is required because the repeated element will be copied

error[E0277]: the trait bound `[Instance; 4]: std::marker::Copy` is not satisfied
  --> src/main.rs:60:21
   |
60 |         instances : [[Instance::new(); 4]; 4],
   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `[Instance; 4]`
   |
   = note: the `Copy` trait is required because the repeated element will be copied

有什么方法可以正确初始化此数组吗？我显然错过了一些东西，但是没有发现 HashSet复制实现可用于数组。也许还有另一种方法可以实现这一目标？

Answer 1

I clearly missed something, but didn't find HashSet copy implementation working with arrays.

那是因为没有一个! Copy表示类型可以逐位复制。像 HashSet<T>这样的类型不可能是这种情况。但是， HashSet<T>是默认可初始化的。结合数组(目前少于32个元素)也可以默认初始化的事实，可以使用以下命令:

let mut m = Matrix {
    instances: Default::default(),
    status: 0,
};

如果您添加

impl Default for Instance {
    fn default() -> Self {
        Self::new()
    }
}

( Permalink to the playground)