동적인 에러 타입
Sometimes we want to allow any type of error to be returned without writing our own enum covering all the different possibilities. The std::error::Error
trait makes it easy to create a trait object that can contain any error.
use std::error::Error; use std::fs; use std::io::Read; fn read_count(path: &str) -> Result<i32, Box<dyn Error>> { let mut count_str = String::new(); fs::File::open(path)?.read_to_string(&mut count_str)?; let count: i32 = count_str.parse()?; Ok(count) } fn main() { fs::write("count.dat", "1i3").unwrap(); match read_count("count.dat") { Ok(count) => println!("개수: {count}"), Err(err) => println!("오류: {err}"), } }
read_count
함수는 std::io::Error
(파일 작업에서) 또는 std::num::ParseIntError
(String::parse
에서)를 반환할 수 있습니다.
Boxing errors saves on code, but gives up the ability to cleanly handle different error cases differently in the program. As such it's generally not a good idea to use Box<dyn Error>
in the public API of a library, but it can be a good option in a program where you just want to display the error message somewhere.
Make sure to implement the std::error::Error
trait when defining a custom error type so it can be boxed. But if you need to support the no_std
attribute, keep in mind that the std::error::Error
trait is currently compatible with no_std
in nightly only.