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用Rust中的结构创建hashmap

rust

-2

carlos.baez · 技术社区 · 6 年前

我正试图建立一个生锈的对象/结构的哈希图…但我不理解这个具体的问题(终生错误)。

#[derive(Hash, Eq, PartialEq)]
#[derive(Serialize, Deserialize, Debug)]
pub struct Node<'a> {
    identifier: &'a str,
    sha_id: Vec<u8>,
    successor_id: Option<Vec<u8>>,
    predecessor_id: Option<Vec<u8>>,
}


impl<'a> Node<'a> {
    ...
    ..
    .
}

pub struct Application<'a> {
    hash_map: HashMap<&'a str, Node>,
}

impl<'a> Application<'a> {
    fn join(&self, node: &Node) {
        self.hash_map.insert(node.identifier, node);
    }
}

错误是中缺少生存期说明符 hash_map: HashMap<&'a str, Node> 我试图解决将节点更改为节点的问题,但在尝试插入时会引发“类型不匹配”错误…

我不明白为什么我会有这个问题错过一生,我也找不到解决办法。

更新:

#[derive(Hash, Eq, PartialEq)]
#[derive(Serialize, Deserialize, Debug)]
pub struct Node<'a> {
    identifier: &'a str,
    sha_id: Vec<u8>,
    successor_id: Option<Vec<u8>>,
    predecessor_id: Option<Vec<u8>>,
}


impl<'a> Node<'a> {
    ...
    ..
    .
}

pub struct Application<'a> {
    hash_map: HashMap<&'a str, Node<'a>>,
}

impl<'a> Application<'a> {
    fn join(&self, node: &Node) {
        self.hash_map.insert(node.identifier, *node);
    }
}

输出为:

"explicit lifetime required in the type of `node`"

更新2:

pub struct Application<'a> {
    hash_map: HashMap<&'a str, Node<'a>>,
}

impl<'a> Application<'a> {
    fn join(&mut self, node: &'a Node<'a>) {
        self.hash_map.insert(node.identifier, *node);
    }

}

输出为:

self.hash_map.insert(node.identifier, *node); cannot move out of borrowed content

完整的解决方案

#[derive(Clone, Hash, Eq, PartialEq)]
#[derive(Serialize, Deserialize, Debug)]
pub struct Node<'a> {
    identifier: &'a str,
    sha_id: Vec<u8>,
    successor_id: Option<Vec<u8>>,
    predecessor_id: Option<Vec<u8>>,
}


impl<'a> Node<'a> {
...
..
.
}

pub struct Application<'a> {
    hash_map: HashMap<&'a str, Node<'a>>,
}

impl<'a> Application<'a> {
    fn join(&mut self, node: Node<'a>) {
        self.hash_map.insert(node.identifier, node);
    }

}

1 回复 | 直到 6 年前

ForceBru 6 年前

这个简化的例子似乎有效:

use std::collections::HashMap;

#[derive(Clone)] // we'll be cloning it later on
struct Node<'a> {
    data: &'a i32 
}


struct Test<'a> {
    hash_map: HashMap<&'a str, Node<'a>>  // the hash map owns the struct
}

impl<'a> Test<'a> {
    fn new() -> Test<'a> {
        Test {hash_map: HashMap::new()}
    }

    fn join(
        &mut self, // must be mutable
        node: Node<'a>) { // do not pass a reference
        self.hash_map.insert("test", node);  // inserting moves `node`
    }
}

fn main() {
    let stuff = Node {data: &12};
    let mut test = Test::new();

    test.join(stuff.clone());  // if we don't clone, `stuff` will get moved

    println!("{}", *test.hash_map["test"].data);  // outputs "12"
}

自从 std::collections::HashMap::insert 试图移动其第二个参数时,不能取消对某个对象的指针的引用并将其传递给此方法,因为否则指针将变为未初始化,这是不允许的。解决这个问题的方法是传递一个移动的值,而不是一个指向 join .