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);
}

我无法将这些连接的字符串转换为&str。我试着把它们放到括号中并拨打.as_str()。没有运气。

我需要HashMap<&str, &str>，因此这里不能选择String。

Answer 1

如果您需要从该函数返回&str，那么您运气不好，请参阅Return local String as a slice (&str)。

如果只是需要将切片放入HashMap并将其向下传递，则需要将String存储在某处并将地图填入地图中String s：

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() {}

我们将&*用于Deref String到str，然后再引用另一个引用，最后到达&str。

请注意，在创建字符串后，必须移动let mut template_partials行，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，因为它使用了两次。

就个人而言，我只使用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() {}

Concat String并将它们转换为＆amp; str

1 个答案: