EitherSwift

Represents a value of one of two possible types (a disjoint union.)
Instances of Either are either an instance of Left or Right.

Description

Swift Either type like scala.util.Either
++ some in \/ - scalaz.\/

Take Right Projection is decided it would be want.

Usage

struct Error {
    var reason: String
    init(_ reason: String) { self.reason = reason }
}
let resultL = Either<Error, String>.left(Error("failed"))
let resultR = Either<Error, String>.right("ok")

isLeft / isRight

resultR.isRight // true
resultR.isLeft  // false

swap(~)

~Either<String, String>.left("failed") ?? "fallback" // failed

getOrElse(??)

// Alias for Right Projection.getOrElse
resultL ?? "fallback" // fallback
resultR ?? "fallback" // success

orElse(|||)

// Right Projection
resultL ||| "ok" // .Right("ok")
Either<Error, String>.left(Error("failed1")) ||| resultL ||| resultR // .Right("ok")

map

// Alias for Right Projection.map
resultR.map { "\($0)!" } // .Right("ok!")
resultL.map { "\($0)!" } // .Left(Error("failed"))

flatMap(>>-)

func isFull<T>(string: String) -> Either<T, Bool> {
    return .right(!string.isEmpty)
}

(resultL >>- isFull).fold(
    { e in e.reason},
    { s in s.description }
)
// failed

(resultR >>- isFull).fold(
    { e in e.reason},
    { s in s.description }
)
// true

Methods

Either<A, B>

• Instance Methods
  • fold<X>(fa: A -> X, _ fb: B -> X) -> X
  • swap() -> Either<B, A>
  • getOrElse(or: () -> B) -> B Right Projection
  • orElse(or: () -> B) -> Either<A, B> Right Projection
  • orElse(or: () -> Either<A, B>) -> Either<A, B> Right Projection
  • map<X>(f: B -> X) -> Either<A, X> Right Projection
  • flatMap<X>(f: B -> Either<A, X>) -> Either<A, X> Right Projection

• Class Methods
  • left(value: A) -> Either<A, B>
  • right(value: B) -> Either<A, B>
  • cond<A, B>(test: Bool, right: () -> B, left: () -> A) -> Either<A, B>

LeftProjection<A, B>

• Instance Methods
  • getOrElse(or: () -> A) -> A
  • foreach<U>(f: A -> U)
  • forall(f: A -> Bool) -> Bool
  • exists(f: A -> Bool) -> Bool
  • map<X>(f: A -> X) -> Either<X, B>
  • flatMap<X>(f: A -> Either<X, B>) -> Either<X, B>
  • filter(p: A -> Bool) -> Either<A, B>?
  • toOption() -> A?

RightProjection<A, B>

• Instance Methods
  • getOrElse(or: () -> B) -> B
  • foreach<U>(f: B -> U)
  • forall(f: B -> Bool) -> Bool
  • exists(f: B -> Bool) -> Bool
  • map<X>(f: B -> X) -> Either<A, X>
  • flatMap<X>(f: B -> Either<A, X>) -> Either<A, X>
  • filter(p: B -> Bool) -> Either<A, B>?
  • toOption() -> B?

Installation

Licence

MIT

Author

to4iki