How to match a String against string literals in Rust?
在Rust中字符串如何匹配？
I'm trying to figure out how to match a String in Rust.
我试图弄清楚Rust中是如何匹配一个字符串类型的。
I initially tried matching like this, but I figured out Rust cannot implicitly cast from std::string::String to &str.
我最初这样尝试，但是我发现Rust不能隐式的从std::string::String转化为&str。
fn main() {
let stringthing = String::from("c");
match stringthing {
"a" => println!("0"),
"b" => println!("1"),
"c" => println!("2"),
}
}
This has the error:
这里的错误：
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`
I then tried to construct new String objects, as I could not find a function to cast a String to a &str.
接着我尝试创建一个新的String对象，因为我不能找到一个方法将String转化为一个&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"),
}
}
This gave me the following error 3 times:
编译器给我提示了如下的错误3次：
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
How to actually match Strings in Rust?
那在Rust中到底是如何匹配String的呢？
You can do something like this:
你可以这样处理：
match &stringthing[..] {
"a" => println!("0"),
"b" => println!("1"),
"c" => println!("2"),
_ => println!("something else!"),
}
There's also an as_str method as of Rust 1.7.0:
在Rust1.7.0之后，你也可以使用as_str方法：
match stringthing.as_str() {
"a" => println!("0"),
"b" => println!("1"),
"c" => println!("2"),
_ => println!("something else!"),
}
stringthing.as_str() is probably the most straightforward of all the answers; I don't like as_ref because it's unnecessarily general, which can lead to bugs, and not as explicit, it isn't completely clear that as_ref() is going to be a &str, as_str is simple and clear.
在所有答案中，stringthing.as_str()方法可能是最直接的。我不喜欢as_ref方法，因为它通常是不必要的，这样做会导致bug并且是不显示的，as_ref()是否会是一个&str类型不是那么清楚，而as_str方法简单明了。
@Zorf You are right. The answer was accepted when as_str did not exist yet. I changed the accepted answer but thank all people who answered this question!
@Zorf 你是正确的。之前as_str不存在时我接受的这个答案。我已经更改了接受的答案，但还是要感谢所有回答这个问题的同学。
