我如何初始化一个数组，以便 Rust 知道它是一个 `String` 数组而不是 `str`? [英] How do I initialize an array so that Rust knows it's an array of `String`s and not `str`?

问题描述

我对 Rust 比较陌生，正在尝试执行以下操作:

I'm relatively new to Rust and am trying to do the following:

pub fn route(request: &[String]) {
    let commands = ["one thing", "another thing", "something else"];

    for command in commands.iter() {
        if command == request {
            // do something
        } else {
            // throw error
        }
    }
}

当我尝试构建它时，我收到一个编译器错误:

When I try to build this, I get a compiler error:

error[E0277]: the trait bound `&str: std::cmp::PartialEq<[std::string::String]>` is not satisfied
 --> src/main.rs:5:20
  |
5 |         if command == request {
  |                    ^^ can't compare `&str` with `[std::string::String]`
  |
  = help: the trait `std::cmp::PartialEq<[std::string::String]>` is not implemented for `&str`
  = note: required because of the requirements on the impl of `std::cmp::PartialEq<&[std::string::String]>` for `&&str`

推荐答案

你应该回去重新阅读 Rust 编程语言，特别是 关于字符串的章节.String 和 &str 是两种不同的类型.

You should go back and re-read The Rust Programming Language, specifically the chapter on strings. String and &str are two different types.

您可以以多种方式创建String，但我通常使用String::from:

You can create Strings in a number of ways, but I commonly use String::from:

let commands = [
    String::from("one thing"),
    String::from("another thing"),
    String::from("something else"),
];

然而，这是低效的，因为您每次都在分配内存.最好是相反的方式，从 &String 到 &str.此外，这并不能解决您的问题，因为您正在尝试将单个值与集合进行比较.我们可以同时解决两个问题:

However, this is inefficient as you are allocating memory each time. It's better to instead go the other way, from &String to &str. Additionally, this doesn't solve your problem because you are attempting to compare a single value to a collection. We can solve both at once:

let commands = ["one thing", "another thing", "something else"];

for command in commands.iter() {
    if request.iter().any(|r| r == command) {
        // do something
    } else {
        // throw error
    }
}

另见:

• Rust 的 `String` 和 `str` 有什么区别?
• 如何直接创建字符串?

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