如何将字符串与字符串文字匹配? [英] How to match a String against string literals?

问题描述

我想弄清楚如何在 Rust 中匹配 String.

I'm trying to figure out how to match a String in Rust.

我最初尝试这样匹配，但我发现 Rust 不能从 std::string::String 隐式转换为 &str.

I initially tried matching like this, but I figured out Rust cannot implicitly cast from std::string::String to &str.

fn main() {
    let stringthing = String::from("c");
    match stringthing {
        "a" => println!("0"),
        "b" => println!("1"),
        "c" => println!("2"),
    }
}

这里有错误:

error[E0308]: mismatched types
 --> src/main.rs:4:9
  |
4 |         "a" => println!("0"),
  |         ^^^ expected struct `std::string::String`, found reference
  |
  = note: expected type `std::string::String`
             found type `&'static str`

然后我尝试构造新的 String 对象，因为我找不到将 String 转换为 &str 的函数.

I then tried to construct new String objects, as I could not find a function to cast a String to a &str.

fn main() {
    let stringthing = String::from("c");
    match stringthing {
        String::from("a") => println!("0"),
        String::from("b") => println!("1"),
        String::from("c") => println!("2"),
    }
}

这给了我 3 次以下错误:

This gave me the following error 3 times:

error[E0164]: `String::from` does not name a tuple variant or a tuple struct
 --> src/main.rs:4:9
  |
4 |         String::from("a") => return 0,
  |         ^^^^^^^^^^^^^^^^^ not a tuple variant or struct

如何在 Rust 中实际匹配 String s?

How to actually match Strings in Rust?

推荐答案

你可以这样做:

match &stringthing[..] {
    "a" => println!("0"),
    "b" => println!("1"),
    "c" => println!("2"),
    _ => println!("something else!"),
}

从 Rust 1.7.0 开始，还有一个 as_str 方法:

There's also an as_str method as of Rust 1.7.0:

match stringthing.as_str() {
    "a" => println!("0"),
    "b" => println!("1"),
    "c" => println!("2"),
    _ => println!("something else!"),
}

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