olbrichj

extension Foo {
    static func promise() -> Promise<FooResult> {
        return PromiseWithDelegate().promise
    }
}

class PromiseWithDelegate: FooDelegate {
    let (promise, seal) = Promise<FooResult>.pending()
    private let foo = Foo()

olbrichj

func attempt<T>(maximumRetryCount: Int = 3, delayBeforeRetry: DispatchTimeInterval = .seconds(2), _ body: @escaping () -> Promise<T>) -> Promise<T> {
    var attempts = 0
    func attempt() -> Promise<T> {
        attempts += 1
        return body().recover { error -> Promise<T> in
            guard attempts < maximumRetryCount else { throw error }
            return after(delayBeforeRetry).then(on: nil, attempt)
        }
    }
    return attempt()

olbrichj

let timeout = after(seconds: 4)

race(when(fulfilled: fetch(url:url)).asVoid(), timeout).then {
    //…
}

olbrichj

let waitAtLeast = after(seconds: 0.3)

firstly {
    fetch(url: url)
}.then {
    waitAtLeast
}.done {
    //…
}

olbrichj

fetch(url: url).then(on: .global(QoS: .userInitiated)) {
    //then closure executes on different thread 
}

olbrichj

firstly {
    when(fulfilled: promise1(), promise2())
}.done { result1, result2 in
    //…
}

olbrichj

firstly {
    fetch(url: url)
}.get { data in
    //…
}.done { data in
    // same data!
}

olbrichj

func fetch(url: URL) -> Promise<Data> {
    return Promise { seal in
        URLSession.shared.dataTask(with: url!) { data, _, error in
            seal.resolve(data, error)
        }.resume()
    }
}

firstly {

olbrichj

firstly {
    fetch(url: url)
}.ensure {
    cleanup()
}.catch {
    handle(error: $0)
}

olbrichj

firstly {
    return fetch(url:url)
}.then{ 
    ...
}