TryFrom and TryInto

类似于 From 和 Into，TryFrom 和 TryInto 是 类型转换的通用 trait。不同于 From/Into 的是，TryFrom 和 TryInto trait 用于易出错的转换，也正因如此，其返回值是 Result 型。

1. use std::convert::TryFrom;
2. use std::convert::TryInto;

4. #[derive(Debug, PartialEq)]
5. struct EvenNumber(i32);

7. impl TryFrom<i32> for EvenNumber {
8. type Error = ();

10. fn try_from(value: i32) -> Result<Self, Self::Error> {
11. if value % 2 == 0 {
12. Ok(EvenNumber(value))
13. } else {
14. Err(())
15. }
16. }
17. }

19. fn main() {
20. // TryFrom

22. assert_eq!(EvenNumber::try_from(8), Ok(EvenNumber(8)));
23. assert_eq!(EvenNumber::try_from(5), Err(()));

25. // TryInto

27. let result: Result<EvenNumber, ()> = 8i32.try_into();
28. assert_eq!(result, Ok(EvenNumber(8)));
29. let result: Result<EvenNumber, ()> = 5i32.try_into();
30. assert_eq!(result, Err(()));
31. }