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fmo91/MinimalPromise.swift

Last active March 9, 2021 07:28
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Revisions

  1. fmo91 revised this gist Jul 11, 2020. 1 changed file with 27 additions and 0 deletions.
    27 changes: 27 additions & 0 deletions MinimalPromise.swift
    View file
    Original file line number Diff line number Diff line change
    @@ -18,6 +18,33 @@ struct Promise<T> {
    }
    }

    static func all(_ promises: [Promise<T>], on queue: DispatchQueue = .main) -> Promise<[T]> {
    return Promise<[T]> { observer in
    let group = DispatchGroup()
    var values = [T]()
    var hasFailed = false
    for promise in promises {
    group.enter()
    promise.then { r in
    switch r {
    case let .success(value):
    values.append(value)
    case let .failure(error):
    observer(.failure(error))
    hasFailed = true
    }
    group.leave()
    }
    }
    group.notify(queue: queue) {
    guard !hasFailed else {
    return
    }
    observer(.success(values))
    }
    }
    }

    func then<E>(_ f: @escaping (T) -> Promise<E>) -> Promise<E> {
    return Promise<E> { observer in
    self.creatorFunction { firstResult in
  2. fmo91 created this gist Jul 4, 2020.
    65 changes: 65 additions & 0 deletions MinimalPromise.swift
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,65 @@
    import Foundation

    struct Promise<T> {
    typealias ResultType = Result<T, Error>
    typealias ResultObserver = (ResultType) -> Void
    typealias CreatorFunction = (@escaping ResultObserver) -> Void
    private let creatorFunction: CreatorFunction

    init(creatorFunction: @escaping CreatorFunction) {
    self.creatorFunction = creatorFunction
    }

    func then<E>(_ f: @escaping (T) -> E) -> Promise<E> {
    return Promise<E> { observer in
    self.creatorFunction { r in
    observer(r.map(f))
    }
    }
    }

    func then<E>(_ f: @escaping (T) -> Promise<E>) -> Promise<E> {
    return Promise<E> { observer in
    self.creatorFunction { firstResult in
    switch firstResult {
    case .success(let successResult):
    f(successResult).creatorFunction { transformedResult in
    observer(transformedResult)
    }
    case .failure(let error):
    observer(.failure(error))
    }
    }
    }
    }

    @discardableResult func then(_ f: @escaping (ResultType) -> Void) -> Self {
    creatorFunction { r in f(r) }
    return self
    }
    }

    func getNumber() -> Promise<Int> {
    return .init { (observer) in
    observer(.success(5))
    }
    }

    func getTextFromNumber(_ number: Int) -> Promise<String> {
    return .init { observer in
    DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) {
    observer(.success("Fernando \(number)"))
    }
    }
    }

    getNumber()
    .then(getTextFromNumber)
    .then { r in
    switch r {
    case .success(let text):
    print(text)
    case .failure(let error):
    print(error)
    }
    }