RustのResult<T, E>型
from Rustの型
rsenum Result<T, E> {
Ok(T),
Err(E),
} is_ok / is_err Result が Ok か Err かを判定する。類似:
isRight / isLeft (Haskell, Either 型)rustlet x: Result<i32, &str> = Ok(10);
assert!(x.is_ok());
let y: Result<i32, &str> = Err("error");
assert!(y.is_err());
Haskell:
haskellisRight :: Either a b -> Bool
isLeft :: Either a b -> Bool---
ok / err Ok(T) の場合は Some(T) , Err(E) の場合は None を返す。rustlet x: Result<i32, &str> = Ok(10);
assert_eq!(x.ok(), Some(10));
let y: Result<i32, &str> = Err("error");
assert_eq!(y.err(), Some("error"));Haskell:
haskellrightToMaybe :: Either a b -> Maybe b
leftToMaybe :: Either a b -> Maybe a
---
map rustlet x: Result<i32, &str> = Ok(10);
let y = x.map(|v| v * 2);
assert_eq!(y, Ok(20)); map_err rustlet x: Result<i32, &str> = Err("error");
let y = x.map_err(|e| format!("wrapped: {}", e));
assert_eq!(y, Err(String::from("wrapped: error"))); and_then Ok(T) の場合、関数を適用して Result<U, E> を返す (flatMap)rustlet x: Result<i32, &str> = Ok(10);
let y = x.and_then(|v| if v > 5 { Ok(v * 2) } else { Err("too small") });
assert_eq!(y, Ok(20)); or_else rustlet x: Result<i32, &str> = Err("error");
let y = x.or_else(|_| Ok(0));
assert_eq!(y, Ok(0)); unwrap / expect Ok(T) の場合は T を返す。 Err(E) の場合は panic。rustlet x: Result<i32, &str> = Ok(10);
assert_eq!(x.unwrap(), 10);
let y: Result<i32, &str> = Err("error");
// y.unwrap(); // panic! unwrap_or Ok(T) の場合は T 、 Err(E) の場合はデフォルト値を返す。rustlet x: Result<i32, &str> = Err("error");
assert_eq!(x.unwrap_or(42), 42);Haskell:
haskellfromRight :: a -> Either b a -> a---
unwrap_or_else Ok(T) の場合は T 、 Err(E) の場合は関数適用した値を返す。rustlet x: Result<i32, &str> = Err("error");
let y = x.unwrap_or_else(|_| 42);
assert_eq!(y, 42);Haskell:
haskellfromRight' :: (e -> a) -> Either e a -> a---
transpose Result<Option<T>, E> を Option<Result<T, E>> に変換する。具体的なsequenceAみたいな
rustlet x: Result<Option<i32>, &str> = Ok(Some(10));
assert_eq!(x.transpose(), Some(Ok(10)));
let y: Result<Option<i32>, &str> = Ok(None);
assert_eq!(y.transpose(), None);
iter Ok(T) の場合 T をイテレートする。rustlet x: Result<i32, &str> = Ok(10);
for v in x.iter() {
println!("{}", v); // 10
}
Haskell:
haskellmaybeToList :: Maybe a -> [a]---
ok_or Option<T> を Result<T, E> に変換する。rustlet x: Option<i32> = Some(10);
assert_eq!(x.ok_or("error"), Ok(10));
let y: Option<i32> = None;
assert_eq!(y.ok_or("error"), Err("error"));
Haskell:
haskellmaybeToEither :: e -> Maybe a -> Either e a---
ok_or_else Option<T> を Result<T, E> に変換するが、 Err の値を関数で生成する。rustlet x: Option<i32> = None;
let y = x.ok_or_else(|| "generated error");
assert_eq!(y, Err("generated error"));Haskell:
haskellmaybeToEither' :: (a -> e) -> Maybe a -> Either e a