Iterator
Runtime errors like connection-refused or file-not-found are handled with the Result
type, but matching this type on every call can be cumbersome. The try-operator ?
is used to return errors to the caller. It lets you turn the common
match some_expression {
Ok(value) => value,
Err(err) => return Err(err),
}
이렇게 짧게 쓸 수 있습니다
some_expression?
이제 우리 예제에 적용해 보겠습니다:
use std::io::Read; use std::{fs, io}; fn read_username(path: &str) -> Result<String, io::Error> { let username_file_result = fs::File::open(path); let mut username_file = match username_file_result { Ok(file) => file, Err(err) => return Err(err), }; let mut username = String::new(); match username_file.read_to_string(&mut username) { Ok(_) => Ok(username), Err(err) => Err(err), } } fn main() { //fs::write("config.dat", "alice").unwrap(); let username = read_username("config.dat"); println!("사용자 이름 또는 오류: {username:?}"); }
This slide should take about 5 minutes.
?
를 사용하도록 read_username
함수를 단순화합니다.
키 포인트:
username
변수는Ok(string)
이거나Err(error)
일 수 있습니다.fs::write
메서드를 사용하여 파일이 없거나, 비었거나, 중복되는 경우 등을 테스트해 봅니다.- Note that
main
can return aResult<(), E>
as long as it implementsstd::process::Termination
. In practice, this means thatE
implementsDebug
. The executable will print theErr
variant and return a nonzero exit status on error.