The ES8 Async/Await control flow for Swift
Swift Ruby
Latest commit f2b45cc Feb 7, 2017 @yannickl committed on GitHub Update README.md

README.md

AwaitKit

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Have you ever dream to write asynchronous code like its synchronous counterpart?

AwaitKit is a powerful Swift library inspired by the Async/Await specification in ES8 (ECMAScript 2017) which provides a powerful way to write asynchronous code in a sequential manner.

Internally it uses PromiseKit to create and manage promises.

RequirementsGetting StartedUsageInstallationContributionContactLicense

Requirements

  • iOS 8.0+
  • Xcode 8.0+
  • Swift 3.0+

Getting Started

If you want have a quick overview of the project take a look to this blog post.

Put simply, write this:

let user = try! await(signIn(username: "Foo", password: "Bar"))
try! await(sendWelcomeMailToUser(user))
try! await(redirectToThankYouScreen())

print("All done!")

Instead of:

signIn(username: "Foo", password: "Bar")
  .then { user in
    return self.sendWelcomeMailToUser(user)
  }
  .then { _ in
    return self.redirectToThankYouScreen()
  }
  .then { _ in
    print("All done!")
  }

Or worse, using the completion block imbrication hell style:

signIn(username: "Foo", password: "Bar") { user in
  self.sendWelcomeMailToUser(user) { _ in
    self.redirectToThankYouScreen() { _ in
      print("All done!")
    }
  }
}

Usage

Async

The async method yields the execution to its closure which will run in a background queue and returns a promise which will be resolved at this end of block.

Here a small example :

func setupNewUser(name: String) -> Promise<User> {  
  return async {
    let newUser = try await(self.createUser(name))
    let friends = try await(self.getFacebookFriends(name))

    newUser.addFriends(friends)

    return newUser
  }
}

Here the setupNewUser returns a promise with a user as value. If the end of async block is executed the promise will be resolved, otherwise if an error occurred inside the async block the promise will be rejected with the corresponding error.

The async block will catch the error thrown to reject the promise so you don't need to manage the await exceptions. But if necessary, you can:

async {
  do {
    try await(self.loginOrThrown(username: "yannickl"))
  }
  catch {
    print(error)
  }

  try await(self.clearCache())
}

Await

The await method will executes the given promise or block and await until it resolved or failed.

do {
  let name: String = try await {
    Thread.sleep(forTimeInterval: 0.2)

    if Int(arc4random_uniform(2) + 1) % 2 == 0 {
      return "yannickl"
    }
    else {
      throw NSError()
    }
  }

  print(name)
}
catch {
  print(error)
}

Custom queues

The async and await methods runs by default on a background concurrent queue. Of course, you can choose your own queues and call the following methods:

DispatchQueue.global(qos: .default).async {

}

try DispatchQueue.global(qos: .default).await {

}

When you use these methods and you are doing asynchronous, be careful to do nothing in the main thread, otherwise you risk to enter in a deadlock situation.

Installation

The recommended approach to use AwaitKit in your project is using the CocoaPods package manager, as it provides flexible dependency management and dead simple installation.

CocoaPods

Install CocoaPods if not already available:

$ [sudo] gem install cocoapods
$ pod setup

Go to the directory of your Xcode project, and Create and Edit your Podfile and add AwaitKit:

$ cd /path/to/MyProject
$ touch Podfile
$ edit Podfile
source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '8.0'
pod 'AwaitKit', '~> 2.0.0'

Install into your project:

$ pod install

If CocoaPods did not find the PromiseKit 4.0.2 dependency execute this command:

$ pod repo update

Open your project in Xcode from the .xcworkspace file (not the usual project file)

$ open MyProject.xcworkspace

Swift Package Manager

You can use The Swift Package Manager to install AwaitKit by adding the proper description to your Package.swift file:

import PackageDescription

let package = Package(
    name: "YOUR_PROJECT_NAME",
    dependencies: [
        .Package(url: "https://github.com/yannickl/AwaitKit.git")
    ]
)

Note that the Swift Package Manager is still in early design and development, for more information checkout its GitHub Page.

Manually

Download the project and copy the AwaitKit folder into your project to use it in. Note that you also need to download the PromiseKit library and import it to your project.

Contribution

Contributions are welcomed and encouraged .

Contact

Yannick Loriot

License (MIT)

Copyright (c) 2016-present - Yannick Loriot

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.