diff options
Diffstat (limited to 'src/lib.rs')
| -rw-r--r-- | src/lib.rs | 59 |
1 files changed, 59 insertions, 0 deletions
@@ -348,6 +348,65 @@ impl<L, R> Either<L, R> { } } + /// Apply the functions `f` and `g` to the `Left` and `Right` variants + /// respectively. This is equivalent to + /// [bimap](https://hackage.haskell.org/package/bifunctors-5/docs/Data-Bifunctor.html) + /// in functional programming. + /// + /// ``` + /// use either::*; + /// + /// let f = |s: String| s.len(); + /// let g = |u: u8| u.to_string(); + /// + /// let left: Either<String, u8> = Left("loopy".into()); + /// assert_eq!(left.map_either(f, g), Left(5)); + /// + /// let right: Either<String, u8> = Right(42); + /// assert_eq!(right.map_either(f, g), Right("42".into())); + /// ``` + pub fn map_either<F, G, M, S>(self, f: F, g: G) -> Either<M, S> + where + F: FnOnce(L) -> M, + G: FnOnce(R) -> S, + { + match self { + Left(l) => Left(f(l)), + Right(r) => Right(g(r)), + } + } + + /// Similar to [`map_either`], with an added context `ctx` accessible to + /// both functions. + /// + /// ``` + /// use either::*; + /// + /// let mut sum = 0; + /// + /// // Both closures want to update the same value, so pass it as context. + /// let mut f = |sum: &mut usize, s: String| { *sum += s.len(); s.to_uppercase() }; + /// let mut g = |sum: &mut usize, u: usize| { *sum += u; u.to_string() }; + /// + /// let left: Either<String, usize> = Left("loopy".into()); + /// assert_eq!(left.map_either_with(&mut sum, &mut f, &mut g), Left("LOOPY".into())); + /// + /// let right: Either<String, usize> = Right(42); + /// assert_eq!(right.map_either_with(&mut sum, &mut f, &mut g), Right("42".into())); + /// + /// assert_eq!(sum, 47); + /// ``` + pub fn map_either_with<Ctx, F, G, M, S>(self, ctx: Ctx, f: F, g: G) -> Either<M, S> + where + F: FnOnce(Ctx, L) -> M, + G: FnOnce(Ctx, R) -> S, + { + match self { + Left(l) => Left(f(ctx, l)), + Right(r) => Right(g(ctx, r)), + } + } + /// Apply one of two functions depending on contents, unifying their result. If the value is /// `Left(L)` then the first function `f` is applied; if it is `Right(R)` then the second /// function `g` is applied. |