将条目添加到 HashMap 并在 for 循环中获取对它们的引用 [英] Adding entries to a HashMap and getting references to them in a for loop
问题描述
我正在尝试在 for
循环中向 HashMap
添加多个元素,但似乎无法正确实现:
I am trying to add multiple elements to a HashMap
in a for
loop but can't seem to get it right:
use std::collections::HashMap;
fn set_if_needed_and_get(hmap: &mut HashMap<String, String>, st: String) -> &String {
hmap.entry(st.clone()).or_insert(st.clone())
}
fn main() {
let meeting_one_email = ["email1", "email2", "email1"];
let mut hmap: HashMap<String, String> = HashMap::new();
let mut attendees: std::vec::Vec<&String> = std::vec::Vec::new();
for m in meeting_one_email.iter() {
attendees.push(set_if_needed_and_get(&mut hmap, m.to_string()));
}
}
我收到错误:
error[E0499]: cannot borrow `hmap` as mutable more than once at a time
--> src/main.rs:14:51
|
14 | attendees.push(set_if_needed_and_get(&mut hmap, m.to_string()));
| ^^^^ mutable borrow starts here in previous iteration of loop
15 | }
16 | }
| - mutable borrow ends here
我知道我不能多次将 hmap
借用为可变的,那么如何在仍然使用 for 循环的同时解决这个问题?使用集合并批量插入可以工作,但我想使用 for 循环.
I understand that I cannot borrow hmap
as mutable more than once, so how can I solve this while still using a for loop? Using a set and inserting in batches would work, but I want to use a for loop.
推荐答案
您的问题不是您试图在循环中向 HashMap
添加元素,而是您正在修改您的 hashmap and 尝试在循环范围内访问您的 hmap
.
Your problem is not that you are trying to add elements to your HashMap
in a loop, it's that you are modifying your hashmap and trying access your hmap
in the scope of the loop.
因为您在 hmap
上有一个可变借用,所以您不能将其元素推送到循环中的 attendees
向量.将值添加到 HashMap
可能需要哈希映射重新分配自身,这会使对其内部值的任何引用无效.
As you have a mutable borrow on hmap
, you are not allowed to push its elements to your attendees
vector in the loop. Adding a value to the HashMap
may require that the hashmap reallocate itself, which would invalidate any references to values inside it.
解决您问题的一个简单方法是:
One easy solution for your problem could be this:
fn main() {
let meeting_one_email = ["email1", "email2", "email1"];
let mut hmap: HashMap<String, String> = HashMap::new();
for m in meeting_one_email.iter() {
set_if_needed_and_get(&mut hmap, m.to_string());
}
let attendees: Vec<&String> = hmap.keys().collect();
}
在此代码中,您正在访问哈希图 填充它以同时填充您的 attendees
向量.
In this code, you are accessing the hashmap after filling it up to also fill your attendees
vector.
这篇关于将条目添加到 HashMap 并在 for 循环中获取对它们的引用的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!