JustTweak

JustTweak is a framework for feature flagging and A/B testing for iOS apps. It provides a simple facade interface interacting with multiple providers that are queried respecting a given priority. Tweaks represent flags used to drive decisions in the client code.

With JustTweak you can achieve the following:

• use a JSON local configuration providing default values for experimentation
• use a number of remote configuration providers such as Firebase and Optmizely to run A/B tests and feature flagging
  
• enable, disable, and customize features locally at runtime
• provide a dedicated UI for customization (this comes particularly handy for feature that are under development to showcase it to stakeholders)

Installation

JustTweak is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "JustTweak"

Implementation

Integration

• define a JSON configuration file including your features (you can use the included

  ExampleConfiguration.json

  as a template)
• define your features and A/B tests in your services such as Firebase and Optmizely (optional)
• configure the JustTweak stack as following

static let tweakManager: TweakManager = {
    // mutable configuration (to override tweaks from other configurations)
    let userDefaultsConfiguration = UserDefaultsConfiguration(userDefaults: UserDefaults.standard)

// remote configurations (optional)
let optimizelyConfiguration = OptimizelyConfiguration()
optimizelyConfiguration.userId = 
let firebaseConfiguration = FirebaseConfiguration()

// local JSON configuration (default tweaks)
let jsonFileURL = Bundle.main.url(forResource: "ExampleConfiguration", withExtension: "json")!
let localConfiguration = LocalConfiguration(jsonURL: jsonFileURL)

// priority is defined by the order in the configurations array (from highest to lowest)
let configurations: [Configuration] = [userDefaultsConfiguration,
                                       optimizelyConfiguration,
                                       firebaseConfiguration,
                                       localConfiguration]
return TweakManager(configurations: configurations)
}()

The order of the objects in the

configurations

The

MutableConfiguration

UserDefaultsConfiguration

TweakViewController

LocalConfiguration

TweakViewController

Usage

The three main features of JustTweak can be accessed from the

TweakManager

1. Checking if a feature is enabled

// check for a feature to be enabled
let enabled = tweakManager.isFeatureEnabled("some_feature")
if enabled {
    // enable the feature
} else {
    // default behaviour
}

1. Get the value of a flag for a given feature.

   TweakManager

   will return the value from the configuration with the highest priority and automatically fallback to the others if no set value is found.

Use either

tweakWith(feature:variable:)

// check for a tweak value
let tweak = tweakManager.tweakWith(feature: "some_feature", variable: "some_flag")
if let tweak = tweak {
    // tweak was found in some configuration, use tweak.value
} else {
    // tweak was not found in any configuration
}

@TweakProperty

@OptionalTweakProperty

TweakManager

@TweakProperty(fallbackValue: ,
               feature: ,
               variable: ,
               tweakManager: )
var labelText: String

@OptionalTweakProperty(fallbackValue: ,
                       feature: ,
                       variable: ,
                       tweakManager: )
var meaningOfLife: Int?

1. Run an A/B test

// check for a tweak value
let variation = tweakManager.activeVariation(for: "some_experiment")
if let variation = variation {
    // act according to the kind of variation (e.g. "control", "variation_1")
} else {
    // default behaviour
}

Caching

The

TweakManager

useCache

• call the

  resetCache

  method on the

  TweakManager

• post a

  TweakConfigurationDidChangeNotification

  notification

Update a configuration at runtime

JustTweak comes with a ViewController that allows the user to edit the

MutableConfiguration

func presentTweakViewController() {
    let tweakViewController = TweakViewController(style: .grouped, tweakManager: )

// either present it modally
let tweaksNavigationController =     UINavigationController(rootViewController:tweakViewController)
tweaksNavigationController.navigationBar.prefersLargeTitles = true
present(tweaksNavigationController, animated: true, completion: nil)

// or push it on an existing UINavigationController
navigationController?.pushViewController(tweakViewController, animated: true)
}

When a value is modified in any

MutableConfiguration

override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.defaultCenter().addObserver(self,
                                                   selector: #selector(updateUI),
                                                   name: TweakConfigurationDidChangeNotification,
                                                   object: nil)
}

@objc func updateUI() {
    // update the UI accordingly
}

Customization

JustTweak comes with three configurations out-of-the-box:

• UserDefaultsConfiguration

  which is mutable and uses

  UserDefaults

  as a key/value store

• LocalConfiguration

  which is read-only and uses a JSON configuration file that is meant to be the default configuration

• EphemeralConfiguration

  which is simply an instance of

  NSMutableDictionary

In addition, JustTweak defines

Configuration

MutableConfiguration

License

JustTweak is available under the Apache 2.0 license. See the LICENSE file for more info.

• Just Eat iOS team