Created
July 22, 2020 05:57
-
-
Save tarunon/9b18557123e6c5a793810f69e76de566 to your computer and use it in GitHub Desktop.
Traits flatMap with FB
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| struct Single<T> {} | |
| struct Maybe<T> {} | |
| protocol MaybeCov { | |
| associatedtype T | |
| func asMaybe() -> Maybe<T> | |
| } | |
| extension Single: MaybeCov { | |
| func asMaybe() -> Maybe<T> { fatalError() } | |
| } | |
| extension Maybe: MaybeCov { | |
| func asMaybe() -> Maybe<T> { fatalError() } | |
| } | |
| @_functionBuilder | |
| struct Builder { | |
| enum Either<First, Second> { | |
| case first(First) | |
| case second(Second) | |
| } | |
| public static func buildBlock() -> Void { | |
| } | |
| public static func buildBlock<C>(_ c: C) -> C { | |
| c | |
| } | |
| public static func buildEither<T, F>(first: T) -> Either<T, F> { | |
| .first(first) | |
| } | |
| public static func buildEither<T, F>(second: F) -> Either<T, F> { | |
| .second(second) | |
| } | |
| } | |
| extension Builder.Either: MaybeCov where First: MaybeCov, Second: MaybeCov, First.T == Second.T { | |
| func asMaybe() -> Maybe<First.T> { | |
| switch self { | |
| case .first(let first): return first.asMaybe() | |
| case .second(let second): return second.asMaybe() | |
| } | |
| } | |
| } | |
| extension Single { | |
| func flatMap<M: MaybeCov>(@Builder _ f: (T) -> M) -> Maybe<M.T> { | |
| f(fatalError() as! T).asMaybe() | |
| } | |
| } | |
| let res = Single<Int>().flatMap { (arg) in | |
| if arg % 2 == 0 { | |
| Single<String>() | |
| } else { | |
| Maybe<String>() | |
| } | |
| } | |
| // res is Maybe<String> |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment