Eventually

A Swift implementation of a Future, which can be used to model and transform asynchronous results while making it easy to bounce results between dispatch queues

Usage

Futures in Eventually can be used to wrap existing APIs, or to create new APIs using Futures

func operation(completion: (Int) -> Void) {
    DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(2)) {
        completion(42)
    }
}

Future<Int> { resolve in
    operation { value
        resolve.success(value)
    }
}.then { result in
    switch result {
    case .success(let value):
        print("value is", value) // "value is 42"
    case .failure(let error):
        print("something went wrong:", error)
    }
}

When initializing a Future the closure receives a "resolver", this resolver is simply a closure that you will call with a FutureResult, a Result enum type which can be either .success or .failure.

There's also a couple of short-hand methods available

func calculateAge() -> Future<Int> {
    // ...
}
calculateAge().success { (value: Int) in
    print("Success value from calling calculateAge() is", value)
}.failure { error in
    print(The Future returned by calculateAge() gave us an error:", error)
}

A non-closure based API for resolving futures is also available

let future = Future<Int>()
future.success { value in
    ...
}
future.resolve(success: age)

Mapping values

With Eventually it is possible to map() one Future type to another, allowing us to compose and transform things easily

calculateAge().map({ (value: Int) -> String in
    return "Age is \(age)"
}).success { value in
    print(value) // "Age is 42"
}

Like always, chaining is possible so multiple transforms can be done

Evaluation Contexts

Most of the methods operating on a Future accepts an EvaluationContext that describes what GCD queue the operation should be called on

Future<String>(on: .background) { resolve
    // Performed on a background queue (eg `DispatchQueue.global(qos: .background)`)
    resolve.success("hello"))
}.map(on: .queue(someCustomQueue)) { value in
    // will be called on the supplied DispatchQueue (`someCustomQueue`)
    return value + " world"
}.map(on: .main) { value in
    // Mapping occurs on the main thread
    let label = UILabel()
    label.text = value
    return text
}.success { label in
    // default is the `.main` context
    self.view.addSubview(label)
}

Installation

Eventually is available as a CocoaPod (pod 'Eventually') and the Swift Package Manager. Framework installation is also available by dragging the Eventually.xcodeproj into your project or via Carthage.

Eventually has no dependencies outside of Foundation and Dispatch (GCD)

License

See the LICENSE file