英文:
How to use vectors and references in nested loops?
问题
我正在尝试使用Rust中的Structs和Vectors来实现父子关系。我遇到的问题是，当我创建一个新的父实例并将其推送到Vector时，它的值会被移动到该Vector中。
在将父项推送到Vector之后尝试添加子项会导致所有权问题。如果将父项推迟到添加子项之后，这个问题就不会发生。
下面链接的Rust播放器是我尝试做的简单示例。实际上，层次结构中还会有另外两个级别（父 -> 子 -> 孙子 -> 曾孙子）。
我尝试使用Box<Parent> 来使用引用并将盒装父项推送到Vec<Box<Parent>>，但是同样的问题会发生，因为引用会被复制，但Parent 没有实现Copy trait。
我想每个Struct实例只复制一次。
#[derive(Debug)]
#[allow(dead_code)]
struct Parent {
id: usize,
children: Vec<Child>,
}
#[derive(Debug)]
#[allow(dead_code)]
struct Child {
id: usize,
age: usize,
}
fn main() {
let mut parents: Vec<Parent> = Vec::new();
for parent_id in 1..4 {
let mut p = Parent {
id: parent_id,
children: Vec::new(),
};
// 如果在这里将其推送到Vector，父项的值就会被移动，
// 并且在下面的子项循环中对`p`的修改将不会传递到外部循环。
parents.push(p);
for child_id in 1..3 {
let c = Child {
id: child_id,
age: child_id + 10,
};
p.children.push(c);
}
// 将推送移到这里可以解决问题，但感觉不太对，必须这样做。
//parents.push(p);
}
println!("{:#?}", parents);
}
错误：
error[E0382]: borrow of moved value: `p`
--> src/main.rs:34:13
|
19 | let mut p = Parent {
| ----- move occurs because `p` has type `Parent`, which does not implement the `Copy` trait
...
27 | parents.push(p);
| - value moved here
...
34 | p.children.push(c);
| ^^^^^^^^^^^^^^^^^^ value borrowed here after move
英文:
I'm trying to implement a parent-child relationship using Structs and Vectors in Rust. The issue I'm having is that when I create a new parent instance and push it to a vector, its value is moved to that vector.
Attempting to add children after pushing the parent into a vector causes an ownership issue. If the parent push is delayed until after adding children this problem doesn't occur.
The Rust playground linked below is a simple example of what I'm trying to do. In reality, there will be another two levels of the hierarchy (parent -> child -> grandchild -> great grandchild).
I've tried using Box<Parent> in an attempt to use references and pushing the boxed parent to a Vec<Box<Parent>> but the same problem occurs where the reference would be copied, but Parent doesn't implement the Copy trait.
I'd like to have one copy of each Struct instance only.
#[derive(Debug)]
#[allow(dead_code)]
struct Parent {
id: usize,
children: Vec<Child>,
}
#[derive(Debug)]
#[allow(dead_code)]
struct Child {
id: usize,
age: usize,
}
fn main() {
let mut parents: Vec<Parent> = Vec::new();
for parent_id in 1..4 {
let mut p = Parent {
id: parent_id,
children: Vec::new(),
};
// If pushed to the vector here, the Parent value is moved
// and the modifications to `p` in the child loop below are
// not seen past the outer loop.
parents.push(p);
for child_id in 1..3 {
let c = Child {
id: child_id,
age: child_id + 10,
};
p.children.push(c);
}
// Moving the push to here works but it doesn't
// feel right having to do this.
//parents.push(p);
}
println!("{:#?}", parents);
}
Error:
error[E0382]: borrow of moved value: `p`
--> src/main.rs:34:13
|
19 | let mut p = Parent {
| ----- move occurs because `p` has type `Parent`, which does not implement the `Copy` trait
...
27 | parents.push(p);
| - value moved here
...
34 | p.children.push(c);
| ^^^^^^^^^^^^^^^^^^ value borrowed here after move
答案1
得分: 1
你可以在完成后将父项推送到它，或者可以通过 Vec 访问它：```rust
parents.push(p);
let p = parents.last_mut().unwrap();
for child_id in 1..3 {
let c = Child {
id: child_id,
age: child_id + 10,
};
p.children.push(c);
}
<details>
<summary>英文:</summary>
You can either push the parent after you're done with it, or you can access it via the `Vec`:
```rust
parents.push(p);
let p = parents.last_mut().unwrap();
for child_id in 1..3 {
let c = Child {
id: child_id,
age: child_id + 10,
};
p.children.push(c);
}
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论