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.
Speaker Notes
This slide should take about 5 minutes.
read_count 함수는 std::io::Error(파일 작업에서) 또는 std::num::ParseIntError(String::parse에서)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.