连接字符串并将它们转换为 &str

Question

fn lyrics_more_bottles(song_template: &mut String, number: i32) {
    let mut template_partials = HashMap::new();
    let mut start_num = number.to_string();
    let mut remaining_num = (number - 1).to_string();

    template_partials.insert("start", start_num + " bottles");
    template_partials.insert("repeat", start_num + " bottles");
    template_partials.insert("remaining", remaining_num + " bottles");
    template_partials.insert("message", "Take one down and pass it around");

    resolve_template(song_template, template_partials);
}

我无法将那些连接的字符串转换为 &str。我试图将它们放在括号中并调用 .as_str()。没有运气。

我需要一个 HashMap<&str, &str>，所以 String 不是一个选项。

Answer 1

如果你需要return函数中的&str，你运气不好，见.

如果你只是需要将切片放入 HashMap 并进一步向下传递，你需要将 String 存储在某个地方并填充参考 Strings:

的地图

use std::collections::HashMap;

fn resolve_template(_: &mut String, _: HashMap<&str, &str>) {}

fn lyrics_more_bottles(song_template: &mut String, number: i32) {
    let mut start_num = number.to_string();
    let mut remaining_num = (number - 1).to_string();

    let start = start_num.clone() + " bottles";
    let repeat = start_num + " bottles";
    let remaining = remaining_num + " bottles";

    let mut template_partials = HashMap::new();

    template_partials.insert("start", &*start);
    template_partials.insert("repeat", &*repeat);
    template_partials.insert("remaining", &*remaining);
    template_partials.insert("message", "Take one down and pass it around");

    resolve_template(song_template, template_partials);
}

fn main() {}

我们使用 &* 到 Deref，String 到 str，然后使用另一个参考以结束 &str。

请注意，let mut template_partials 行必须在创建 字符串后移动 ，否则当删除字符串时，映射可能包含对无效内存的引用。此外，start_num 需要克隆，因为它被使用了两次。

就个人而言，我只是使用 format! 并使用相同的字符串两次，而不是克隆和修改它两次：

use std::collections::HashMap;

fn resolve_template(_: &mut String, _: HashMap<&str, &str>) {}

fn lyrics_more_bottles(song_template: &mut String, number: i32) {
    let start_and_repeat = format!("{} bottles", number);
    let remaining = format!("{} bottles", number - 1);

    let mut template_partials = HashMap::new();

    template_partials.insert("start", &*start_and_repeat);
    template_partials.insert("repeat", &*start_and_repeat);
    template_partials.insert("remaining", &*remaining);
    template_partials.insert("message", "Take one down and pass it around");

    resolve_template(song_template, template_partials);
}

fn main() {}

连接字符串并将它们转换为 &str

Concat String and convert them to &str

string

concat

rust