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Swift On Device Evaluation

info

On-device evaluation sdks are for Enterprise and Pro Tier companies only. If you are trying to follow these instructions but do not meet that criteria, some of the setup steps may not work.

The SwiftOnDeviceEvaluations SDK uses a different paradigm then its precomputed counter part (Swift Precomputed Evaluations SDK). It is a Client SDK that behaves more like a Server SDK. Rather than requiring a user up front, you can check gates/configs/experiments for any set of user properties, because the SDK downloads a complete representation of your project and evaluates checks in real time.

Pros​

  • No need for a network request when changing user properties - just check the gate/config/experiment locally
  • Can bring your own cdn or synchronously initialize with a preloaded project definition
  • Lower latency to download configs cached at the edge, rather than evaluated for a given user (which cannot be cached as much)

Cons​

  • Entire project definition is available client side - the names and configurations of all experiments and feature flags accessible by your client key are exposed.
  • Payload size is strictly larger than what is required for the Swift Precomputed Evaluations SDK.
  • Evaluation performance is slightly slower - rather than looking up the value, the SDK must actually evaluate targeting conditions and an allocation decision
  • Does not support ID list segments with > 1000 IDs
  • Does not support IP or User Agent based checks (Browser Version/Name, OS Version/Name, IP, Country)

Installation​

To use the SDK in your project, you must add Statsig as a dependency.

In your Xcode, select File > Swift Packages > Add Package Dependency and enter the URL https://github.com/statsig-io/swift-on-device-evaluations-sdk.git.

You can also include it directly in your project's Package.swift. Find out the latest release version on our GitHub page.

//...
dependencies: [
    // see the latest version on https://github.com/statsig-io/swift-on-device-evaluations-sdk/releases
    .package(url: "https://github.com/statsig-io/swift-on-device-evaluations-sdk.git", .upToNextMinor("X.Y.Z")),
],
//...
targets: [
    .target(
        name: "YOUR_TARGET",
        dependencies: ["StatsigOnDeviceEvaluations"]
    )
],
//...

Initialize the SDK​

Initialize the SDK using a Client SDK key from the "API Keys" tab on the Statsig console. When creating the key, or using an existing key, you will need to add the "Allow Download Config Specs" scope. Client keys, by default, are not able to download the project definition to do on device evaluation. You must opt in to allow your client key to access your full project definition on our cdn.

When creating a new client key, select "Allow Download Config Specs"

Add DCS Scope to Existing Key

caution

Do NOT embed a Server Secret Key in client side applications.

import StatsigOnDeviceEvaluations

 // (optional) Configure the SDK if needed
let opts = StatsigOptions()
opts.environment.tier = "staging"

Statsig.shared.initialize("client-sdk-key", options: opts) { err in
    if let err = err {
        print("Error \(err)")
    }
}

// or, create your own instance

let myStatsigInstance = Statsig()
myStatsigInstance.initialize("client-sdk-key", options: opts) { err in
    if let err = err {
        print("Error \(err)")
    }
}


// or, with Objective C

StatsigOptions *options = [StatsigOptions new];

StatsigEnvironment *env = [StatsigEnvironment new];
env.tier = @"staging";
options.environment = env;

[[Statsig sharedInstance] 
  initializeWithSDKKey:@"client-sdk-key"
  options:options
  completion:^(NSError * _Nullable error) {
    if (error != nil) {
        NSLog(@"Error %@", error);
    }
}];

Working with the SDK​

Checking a Feature Flag/Gate​

Now that your SDK is initialized, let's check a Feature Gate. Feature Gates can be used to create logic branches in code that can be rolled out to different users from the Statsig Console. Gates are always CLOSED or OFF (think return false;) by default.

// Simple Pass/Fail check

let isPassing: Bool = Statsig.shared.checkGate("my_gate", user)


// or, the verbose FeatureGate check

let gate = Statsig.shared.getFeatureGate("my_gate", user)
print(gate.evaluationDetails.reason) // "Network" | "Cache" | "Unrecognized"
let isPassing: Bool = gate.value;


// or, using Objective C

BOOL isPassing = [[Statsig sharedInstance] checkGate:@"my_gate" forUser:user];

Reading a Dynamic Config​

Feature Gates can be very useful for simple on/off switches, with optional but advanced user targeting. However, if you want to be able send a different set of values (strings, numbers, and etc.) to your clients based on specific user attributes, e.g. country, Dynamic Configs can help you with that. The API is very similar to Feature Gates, but you get an entire json object you can configure on the server and you can fetch typed parameters from it. For example:

let config = Statsig.shared.getDynamicConfig("my_dynamic_config", user)

let name: String? = config.value["product_name"] as? String
let price: Double? = config.value["price"] as? Double

Getting an Layer/Experiment​

Then we have Layers/Experiments, which you can use to run A/B/n experiments. We offer two APIs, but we recommend the use of layers to enable quicker iterations with parameter reuse.

// Getting values via getLayer

let layer = Statsig.shared.getLayer("my_layer", user)
let name: String? = layer.getValue(param: "product_name", fallback: "Unknown") as? String


// or, using getExperiment

let experiment = Statsig.shared.getExperiment("my_experiment", user)

let name: String? = experiment.value["product_name"] as? String
let price: Double? = experiment.value["price"] as? Double

Logging an Event​

Now that you have a Feature Gate or an Experiment set up, you may want to track some custom events and see how your new features or different experiment groups affect these events. This is super easy with Statsig - simply call the Log Event API for the event, and you can additionally provide some value and/or an object of metadata to be logged together with the event:

let event = StatsigEvent(
    eventName: "add_to_cart",
    value: "SKU_1234",
    metadata: [
        "price": "9.99",
        "item_name": "CoolProduct"
    ]
)

Statsig.shared.logEvent(event, user)

Learn more about identifying users, group analytics, and best practices for logging events in the logging events guide.

Code Examples​

Prefer seeing it in practice? Included in the open source repository are some Code Examples. View these for common use cases for the SDK. Included are both Swift and Objective C uses.

Statsig User​

You need to provide a StatsigUser object to check/get your configurations. You should pass as much information as possible in order to take advantage of advanced gate and config conditions.

Most of the time, the userID field is needed in order to provide a consistent experience for a given user (see logged-out experiments to understand how to correctly run experiments for logged-out users).

Besides userID, we also have email, ip, userAgent, country, locale and appVersion as top-level fields on StatsigUser. In addition, you can pass any key-value pairs in an object/dictionary to the custom field and be able to create targeting based on them.

let user = StatsigUser(
    userID: "a-user",
    customIDs: ["EmployeeID": "an-employee"],
    email: "user@statsig.io",
    ip: "58.84.239.246",
    userAgent: "Mozilla/5.0 (iPad; CPU OS 13_4_1....",
    country: "NZ",
    locale: "en_NZ",
    appVersion: "3.2.1",
    custom: ["Level": "9001"],
    privateAttributes: ["SensitiveInfo": "shhh"]
)

Private Attributes​

Have sensitive user PII data that should not be logged? No problem, we have a solution for it! On the StatsigUser object we also have a field called privateAttributes, which is a simple object/dictionary that you can use to set private user attributes. Any attribute set in privateAttributes will only be used for evaluation/targeting, and removed from any logs before they are sent to Statsig server.

For example, if you have feature gates that should only pass for users with emails ending in "@statsig.com", but do not want to log your users' email addresses to Statsig, you can simply add the key-value pair { email: "my_user@statsig.com" } to privateAttributes on the user and that's it!

Setting a Global User​

To avoid needing to pass the user object to every single evaluation call, you can set a global user. This user will be used for all evaluations unless otherwise specified.

Statsig.shared.setGlobalUser(myGlobalUser)

Statsig.shared.checkGate("my_gate") // <- Will use myGlobalUser
Statsig.shared.checkGate("my_gate", StatsigUser(userID: "user-123")) // <- Will NOT use myGlobalUser

Statsig Options​

You can configure certain aspects of the SDKs behavior by passing a StatsigOptions object during initialization.

  • eventQueueMaxSize: Int, default 20

    • The maximum number of events to batch before flushing logs to the server.

  • eventQueueInternalMs: Double, default 10,000

    • How frequently to flush queued logs.

  • eventLoggingAPI: String, default https://events.statsigapi.net/v1/rgstr

    • The API where all events are sent.

  • configSpecAPI: Int, default https://api.statsigcdn.com/v1/download_config_specs/

    • The API used to fetch the latest configurations.

  • environment: StatsigEnvironment, default {}

    • An object you can use to set environment variables that apply to all of your users in the same session and will be used for targeting purposes.

Shutting Statsig Down​

In order to save users' data and battery usage, as well as prevent logged events from being dropped, we keep event logs in client cache and flush periodically. Because of this, some events may not have been sent when your app shuts down.

To make sure all logged events are properly flushed or saved locally, you should tell Statsig to shutdown when your app is closing:

Statsig.shared.shutdown { err in
    if let err = err {
        print("An error occurred during Statsig shutdown: \(err)")
    } else {
        print("Statsig shutdown successfully")
    }
}

Post Init Syncing​

From Network​

By default, the SDK will only sync during initialization. If you would like to re-sync after initialization, you can call the Statsig.update method. This will trigger a network call to fetch the latest changes from the server.

Statsig.shared.update { err in
    if let err = err {
        print("Statsig update error: \(err)")
    }
}

From a Local File​

If you maintain your own copy of the "specs" json, you can pass it in to the update with Statsig.updateSync(). This will skip the network call and use the provided specs instead.

let result = Statsig.shared.updateSync(updatedSpecs: myJsonData)

Scheduled Polling​

If you would like the SDK to regularly poll for updates, you can start the polling task with Statsig.scheduleBackgroundUpdates(). This will call Statsig.update internally, hitting the network and pulling down the latest changes.

let pollingTask = Statsig.shared.scheduleBackgroundUpdates() // Defaults to 1 hour interval

// or, specify a custom interval
let pollingTask = Statsig.shared.scheduleBackgroundUpdates(intervalSeconds: 300)

// and, if you need to cancel it later
pollingTask?.cancel()

Local Overrides​

It is possible to override the values returned by the Statsig SDK. This can be useful in unit testing or for enabling features for local development.

To get setup with local overrides, you can use pass an instance of LocalOverrideAdapter to the SDK via the StatsigOptions object.

Note: it is possible to write your own override adapter. You can implement the OverrideAdapter protocol and pass that in instead.

let user = StatsigUser(userID: "a-user")

let overrides = LocalOverrideAdapter()

// Override a gate
overrides.setGate(user, FeatureGate.create("local_override_gate", true))

// Override a dynamic config (Similar for Layer and Experiment)
overrides.setDynamicConfig(user, DynamicConfig.create("local_override_dynamic_config", ["foo": "bar"]))

let opts = StatsigOptions()
opts.overrideAdapter = overrides

Statsig.shared.initialize(YOUR_SDK_KEY, options: opts) { _ in
    let gate = Statsig.shared.getFeatureGate("local_override_gate", user)
    print("Result: \(gate.value) (\(gate.evaluationDetails.reason))")
}

FAQ​

How do I run experiments for logged out users?​

See the guide on device level experiments