如何从铁锈中的函数返回其属性具有&str类型的结构？

Question

我试图做以下几件事

// Just removes redundant white space while also splitting the string
// with a whitespace.
fn split_whitespace(string: &str) -> Vec<&str> {
    let words: Vec<&str> = string
        .split_whitespace()
        .filter(|&word| word != "")
        .collect();
    words
}

pub fn get_websites_from_hosts(hosts_path: &Path) -> Result<Vec<Website>, std::io::Error> {
    let hosts_string = read_to_string(hosts_path)?;

    let result: Vec<Website> = hosts_string
        .lines()
        .filter(|&line| split_whitespace(&line.to_owned()).len() == 2)
        .map(|line| {
            let ip_domain = split_whitespace(&line.to_owned());
            Website {
                domain_name: ip_domain[1], // This won't work because it is refering hosts_string which is a local variable of the function
                redirect_ip: ip_domain[0], // the same case with this one.
                is_blocked: true,
                hosts_path,
            }
        })
        .collect();

    Ok(result)
}

我想要实现的是成功地返回网站结构，而可能没有编辑结构声明。

这是网站结构声明

#[derive(Debug, Clone)]
pub struct Website<'a> {
    pub domain_name: &'a str,
    pub redirect_ip: &'a str,
    pub is_blocked: bool,
    pub hosts_path: &'a Path,
}

这是一个错误

error[E0515]: cannot return value referencing temporary value
  --> src/parser.rs:21:13
   |
20 |               let ip_domain = split_whitespace(&line.to_owned());
   |                                                 --------------- temporary value created here
21 | /             Website {
22 | |                 domain_name: ip_domain[1],
23 | |                 redirect_ip: ip_domain[0],
24 | |                 is_blocked: true,
25 | |                 hosts_path,
26 | |             }
   | |_____________^ returns a value referencing data owned by the current function

For more information about this error, try `rustc --explain E0515`.
error: could not compile `website-blocker` due to previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `website-blocker` due to previous error

我希望在遇到这个和类似的问题时，能有一个深刻的解释和一般的提示。

Answer 1

结构中的&str引用引用read_to_string返回的字符串段。该字符串(hosts_string)在fn get_websites_from_hosts的末尾被删除和解除分配，因此如果您可以返回对它的引用，它们将处于悬空状态。生锈阻止你做那件事。

相反，您需要将read_to_string移出该函数，并将字符串作为&str传入，或者更改您的结构以保存String、IpAddr等拥有的值。

#[derive(Debug, Clone)]
pub struct Website<'a> {
    pub domain_name: String,
    pub redirect_ip: IpAddr,
    pub is_blocked: bool,
    pub hosts_path: &'a Path,
}

如果要避免某些String分配，可以使用“小字符串优化”库(如compact_str )。

#[derive(Debug, Clone)]
pub struct Website<'a> {
    // Stores a domain name of up to 24 bytes in place,
    // without an extra heap allocation
    pub domain_name: CompactString,
    pub redirect_ip: IpAddr,
    pub is_blocked: bool,
    pub hosts_path: &'a Path,
}