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. }