错误处理

可恢复错误与 Result

use std::fs::File;

fn main() {
    // f 类型 Result<File,Error>
    let f = File::open("hello.txt");

    let f = match f {
        Ok(file) => file,
        Err(error) => {
            panic!("There was a problem opening the file: {:?}", error);
        }
    };
}

匹配不同的错误

// #[derive(Debug)]

use std::fs::File;
use std::io::ErrorKind;

fn main() {
    // f 类型 Result<File,Error>
    let f = File::open("hello.txt");

    let f = match f {
        Ok(file) => file,
        Err(error) => match error.kind() {
            ErrorKind::NotFound => match File::create("hello.txt") {
                Ok(fc) => fc,
                Err(e) => panic!("Tried to create file but there was a problem:{:?}", e),
            },
            other_error => panic!("There was a problem opening the file: {:?}", other_error),
        },
    };
}

失败时触发 panic 的快捷⽅式：unwrap 和 expect

use std::fs::File;

fn main() {
    // unwrap 方式，如果错则打印错误，否则返回正确的file
    let f = File::open("hello.txt").unwrap();

    // 传入panic错误信息
    let f = File::open("hello.txt").expect("Failed to open hello.txt");
}

传播错误

use std::fs::File;
use std::io;
use std::io::Read;

fn read_username_from_file() -> Result<String, io::Error> {
    let f = File::open("hello.txt");

    let mut f = match f {
        Ok(file) => file,
        Err(e) => return Err(e),
    };
    let mut s = String::new();

    match f.read_to_string(&mut s) {
        Ok(_) => Ok(s),
        Err(e) => Err(e),
    }
}