rust - 如何从 env::var 返回匹配的值？

Question

如果找到环境变量SOMEVALUE，它应该绑定(bind)到k:

let k = match env::var(SOMEVALUE) {
    Ok(val) => {return val},
    Err(e) => println!("could not find {}: {}", SOMEVALUE, e),
};

编译这段代码会出现以下错误

   |
11 |         Ok(val) => {return val},
   |                            ^^^ expected (), found struct `std::string::String`
   |
   = note: expected type `()`
              found type `std::string::String`

Answer 1

Victor 写的是正确的，但您可能想实际绑定(bind)一个值到 k；在这种情况下，您应该将代码更改为:

let k = match env::var(SOMEVALUE) {
    Ok(val) => val,
    Err(e) => panic!("could not find {}: {}", SOMEVALUE, e),
};

等效地，您可以使用 Result::unwrap_or_else :

let k = env::var(SOMEVALUE).unwrap_or_else(|e| {
    panic!("could not find {}: {}", SOMEVALUE, e)
});