• Result type
  • Option type
  • What to do with Result or Option
    • Success: use the value
    • Failure: recover
  • Recoverable => Unrecoverable

testing methods

  • Result
    • is_ok
    • is_err
  • Option
    • is_some
    • is_none

Result to Option

  • ok method
    • Ok(T).ok() -> Some(T)
    • Err(E).ok() -> None

Option to Result

  • ok_or method
    • Some(T).ok_or(err_value) -> Ok(T)
    • None.ok_or(err_value) -> Err(err_value)

fallback

  • Ok(T).unwrap_or(fallback) -> T
  • Some(T).unwrap_or(fallback) -> T
  • Err(E).unwrap_or(fallback) -> fallback
  • None.unwrap_or(fallback) -> fallback

unwrap_or_default

  • calls the default function from the Default trait

Transform Ok or Some values only

  • Ok(T).map(|v| v.operation()) -> T.operation()
  • Some(T).map(|v| v.operation()) -> T.operation()
  • Err(E).map(…) -> Err(E)
  • None.map(…) -> None
  1. fn main() {
  2.     let v = Version{
  3.         id: 123,
  4.         published_by: Some(12),
  5.     };
  6.     let u = v.published_by();
  7.     println!("{:?}", u);
  8. }
  10. #[derive(Debug)]
  11. struct Version {
  12.     id: i32,
  13.     published_by: Option<i32>,
  14. }
  16. #[derive(Debug)]
  17. struct User {
  18.     id: i32,
  19.     login: String,
  20. }
  22. impl User {
  23.     fn find(id: i32) -> Self {
  24.         User {
  25.             id: 1,
  26.             login: String::from("hello")
  27.         }
  28.     }
  29. }
  31. impl Version {
  32.     pub fn published_by(&self) -> Option<User> {
  33.         self.published_by.map(|p| User::find(p))
  34.     }
  35. }