通过迭代哈希图创建向量

Question

Rust迭代a HashMap并将结果收集到a中的可选方式是Vec什么？到目前为止，这是我的尝试：

use std::collections::HashMap;

struct User {
    reference: String,
    email: String
}

fn main() {

    let mut users: HashMap<String, User> = HashMap::new();
    users.insert("first".to_string(), User { reference: "ref1".to_string(), email: "test@test.com".to_string() });
    users.insert("second".to_string(), User { reference: "ref2".to_string(), email: "test1@test.com".to_string() });
    users.insert("third".to_string(), User { reference: "ref3".to_string(), email: "test3@test.com".to_string() });

    //this is my failed attempt
    let user_refs: Vec<String> = users.iter().map(|(_, user)| &user.reference.clone()).collect();

}

引发错误

src/main.rs:15:85: 15:94 error: the trait `core::iter::FromIterator<&collections::string::String>` is not implemented for the type `collections::vec::Vec<collections::string::String>` [E0277]
src/main.rs:15  let user_refs: Vec<String> = users.iter().map(|(_, user)| &user.reference.clone()).collect();
                                                                                                   ^~~~~~~~~
src/main.rs:15:85: 15:94 note: a collection of type `collections::vec::Vec<collections::string::String>` cannot be built from an iterator over elements of type `&collections::string::String`
src/main.rs:15  let user_refs: Vec<String> = users.iter().map(|(_, user)| &user.reference.clone()).collect();
                                                                                                   ^~~~~~~~~
error: aborting due to previous error

Answer 1

您产生的Vec需要拥有字符串，因此请删除&之前的user.reference.clone()。

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