Experiment iOS SDK

Official documentation for Amplitude Experiment's Client-side iOS SDK implementation.

Install¶

pod 'AmplitudeExperiment', '~> <VERSION>'

// (1) Initialize the experiment client with Amplitude Analytics
let experiment = Experiment.initializeWithAmplitudeAnalytics(
    apiKey: "DEPLOYMENT_KEY",
    config: ExperimentConfigBuilder().build()
)

// (2) Start the SDK
experiment.start() { error in

    // (3) Lookup a flag's variant
    let variant = experiment.variant("FLAG_KEY")
    if variant.value == "on" {
        // Flag is on
    } else {
        // Flag is off
    }
}

// (1) Initialize the experiment client and implement a
//     custom exposure tracking provider.
class ExposureTracker: ExposureTrackingProvider {
    func track(exposure: Exposure) {
        // TODO: Implement exposure tracking
        // analytics.track(name: "$exposure", properties: [
        //     "flag_key": exposure.flagKey,
        //     "variant": exposure.variant,
        //     "experiment_key": exposure.experimentKey
        // ])
    }
}
let experiment = Experiment.initialize(
    apiKey: "DEPLOYMENT_KEY",
    config: ExperimentConfigBuilder()
        .exposureTrackingProvider(ExposureTracker())
        .build()
)
// (2) Start the SDK with the user.
let user = ExperimentUserBuilder()
    .userId("user@company.com")
    .deviceId("abcdefg")
    .userProperty("premium", value: true)
    .build()
experiment.start(user) { error in

    // (3) Lookup a flag's variant
    let variant = experiment.variant("FLAG_KEY")
    if variant.value == "on" {
        // Flag is on
    } else {
        // Flag is off
    }
}

Core functions¶

The following functions make up the core of the Experiment client-side SDK.

Initialize¶

The SDK client should be initialized in your application on startup. The deployment key argument passed into the apiKey parameter must live within the same project that you are sending analytics events to.

func initializeWithAmplitudeAnalytics(
    apiKey: String,
    config: ExperimentConfig
) -> ExperimentClient

func initialize(apiKey: String, config: ExperimentConfig) -> ExperimentClient

The initializer returns a singleton instance, so subsequent initializations for the same instance name will always return the initial instance. To create multiple instances, use the instanceName configuration.

let experiment = Experiment.initializeWithAmplitudeAnalytics(
    apiKey: "DEPLOYMENT_KEY",
    config: ExperimentConfigBuilder().build()
)

// (1) Initialize the experiment client and implement a
//     custom exposure tracking provider.
class ExposureTracker: ExposureTrackingProvider {
    func track(exposure: Exposure) {
        // TODO: Implement exposure tracking
        // analytics.track(name: "$exposure", properties: [
        //     "flag_key": exposure.flagKey,
        //     "variant": exposure.variant,
        //     "experiment_key": exposure.experimentKey
        // ])
    }
}
let experiment = Experiment.initialize(
    apiKey: "DEPLOYMENT_KEY",
    config: ExperimentConfigBuilder()
        .exposureTrackingProvider(ExposureTracker())
        .build()
)

Configuration¶

The SDK client can be configured once on initialization.

Integrations¶

If you use either Amplitude or Segment Analytics SDKs to track events into Amplitude, you'll want to set up an integration on initialization. Integrations automatically implement provider interfaces to enable a more streamlined developer experience by making it easier to manage user identity and track exposures events.

Amplitude.instance().initializeApiKey("API_KEY")
let experiment = Experiment.initializeWithAmplitudeAnalytics(
    apiKey: "DEPLOYMENT_KEY",
    config: ExperimentConfigBuilder().build()
)

class SegmentExposureTrackingProvider : ExposureTrackingProvider {
    private let analytics: Analytics
    init(analytics: Analytics) {
        self.analytics = analytics
    }
    func track(exposure: Exposure) {
        analytics.track("$exposure", properties: [
            "flag_key": exposure.flagKey,
            "variant": exposure.variant,
            "experiment_key": exposure.experimentKey
        ])
    }
}

let analytics = // Initialize segment analytics
ExperimentConfig config = ExperimentConfigBuilder()
    .exposureTrackingProvider(SegmentExposureTrackingProvider(analytics))
    .build()
let experiment = Experiment.initialize(apiKey: "<DEPLOYMENT_KEY>", config: config)

let userId = SEGState.sharedInstance().userInfo.userId
let deviceId = SEGState.sharedInstance().userInfo.anonymousId

let user = ExperimentUserBuilder()
    .userId(userId)
    .deviceId(deviceId)
    .build()
experiment.fetch(user: user, completion: nil)

Start¶

Start the SDK by getting flag configurations from the server and fetching remote evaluation variants for the user. The SDK is ready once the completion callback is called.

func start(_ user: ExperimentUser? = nil, completion: ((Error?) -> Void)? = nil)

Call start() when your application is initializing, after user information is available to use to evaluate or fetch variants. The provided completion block is called after loading local evaluation flag configurations and fetching remote evaluation variants.

Configure the behavior of start() by setting fetchOnStart in the SDK configuration on initialization to improve performance based on the needs of your application.

• If your application never relies on remote evaluation, set fetchOnStart to false to avoid increased startup latency caused by remote evaluation.
• If your application relies on remote evaluation, but not right at startup, you may set fetchOnStart to false and call fetch() separately.

experiment.start() { error in 
    // SDK Started
}

let user = ExperimentUserBuilder()
    .userId("user@company.com")
    .deviceId("abcdefg")
    .userProperty("premium", value: true)
    .build()
experiment.start(user) { error in
    // SDK Started
}

Fetch¶

Fetches variants for a user and store the results in the client for fast access. This function remote evaluates the user for flags associated with the deployment used to initialize the SDK client.

func fetch(user: ExperimentUser?, options: FetchOptions?, completion: ((ExperimentClient, Error?) -> Void)?)

Amplitude Experiment recommends calling fetch() during application start up so that the user gets the most up-to-date variants for the application session. Furthermore, you'll need to wait for the fetch request to return a result before rendering the user experience to avoid the interface "flickering".

let user = ExperimentUserBuilder()
    .userId("user@company.com")
    .userProperty("premium", value: true)
    .build()
experiment.fetch(user: user) { experiment, error in
    // Do something...
}

If you're using an integration or a custom user provider then you can fetch without inputting the user.

experiment.fetch(user: nil, completion: nil)

Variant¶

Access a variant for a flag or experiment from the SDK client's local store.

func variant(_ key: String, fallback: Variant? = nil) -> Variant

When determining which variant a user has been bucketed into, you'll want to compare the variant value to a well-known string.

let variant = experiment.variant("<FLAG_KEY>")
if variant.value == "on" {
    // Flag is on
} else {
    // Flag is off
}

let variant = client.variant("<FLAG_KEY>")
if variant.value == "on" {
    if let payload = variant.payload as? [String:String] {
        let value = payload["key"]
    }
}

A null variant value means that the user hasn't been bucketed into a variant. You may use the built in fallback parameter to provide a variant to return if the store doesn't contain a variant for the given flag key.

let variant = experiment.variant("<FLAG_KEY>", fallback: Variant("control"))
if variant.value == "control" {
    // Control
} else if variant.value == "treatment" {
    // Treatment
}

All¶

Access all variants stored by the SDK client.

func all() -> [String:Variant]

Clear¶

Clear all variants in the cache and storage.

func clear()

You can call clear after user logout to clear the variants in cache and storage.

experiment.clear()

Exposure¶

Manually track an exposure event for the current variant of the given flag key through configured integration or custom exposure tracking provider. Generally used in conjunction with setting the automaticExposureTracking configuration optional to false.

func exposure(key: String)

let variant = experiment.variant("<FLAG_KEY>")

// Do other things...

experiment.exposure("<FLAG_KEY>")
if variant.value == "control" {
    // Control
} else if variant.value == "treatment" {
    // Treatment
}

Providers¶

Provider implementations enable a more streamlined developer experience by making it easier to manage user identity and track exposures events.

User provider¶

The user provider is used by the SDK client to access the most up-to-date user information only when it's needed (for example: when fetch() is called). This provider is optional, but helps if you have a user information store already set up in your application. This way, you don't need to manage two separate user info stores in parallel, which may result in a divergent user state if the application user store is updated and experiment isn't (or via versa).

protocol ExperimentUserProvider {
    func getUser() -> ExperimentUser
}

To use your custom user provider, set the userProvider configuration option with an instance of your custom implementation on SDK initialization.

let config = ExperimentConfigBuilder()
    .userProvider(CustomUserProvider())
    .build()
let experiment = Experiment.initialize(apiKey: "<DEPLOYMENT_KEY>", config: config)

Exposure tracking provider¶

Implementing an exposure tracking provider is highly recommended. Exposure tracking increases the accuracy and reliability of experiment results and improves visibility into which flags and experiments a user is exposed to.

protocol ExposureTrackingProvider {
    func track(exposure: Exposure)
}

The implementation of track() should track an event of type $exposure (a.k.a name) with two event properties, flag_key and variant, corresponding to the two fields on the Exposure object argument. Finally, the event tracked must eventually end up in Amplitude Analytics for the same project that the [deployment] used to initialize the SDK client lives within, and for the same user that variants were fetched for.

To use your custom user provider, set the exposureTrackingProvider configuration option with an instance of your custom implementation on SDK initialization.

ExperimentConfig config = ExperimentConfigBuilder()
    .exposureTrackingProvider(CustomExposureTrackingProvider(analytics))
    .build()
let experiment = Experiment.initialize(apiKey: "<DEPLOYMENT_KEY>", config: config)