Swift On Device Evaluation SDK

Source code: statsig-io/swift-on-device-evaluations-sdk

Statsig’s normal (remote evaluation) SDKs are recommended for most client applications. Understand the use case and privacy risks by reading the On-Device Eval SDK overview. On-device evaluation SDKs are for Enterprise & Pro Tier only.

These SDKs use a different paradigm than their precomputed counterparts: JS, Android, iOS, they behave more like Server SDKs. 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. See our client key with server permission best practices
Payload size is strictly larger than what is required for the traditional SDKs
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)

Set Up the SDK

Install the SDK

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:
// https://github.com/statsig-io/swift-on-device-evaluations-sdk/releases

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

Next, initialize the SDK with a client SDK key from the “API Keys” tab on the Statsig console. These keys are safe to embed in a client application.Along with the key, pass in a User Object with the attributes you’d like to target later on in a gate or experiment.

For On-Device Evaluation, you’ll need to add the “Allow Download Config Specs” scope. Client keys, by default, are not able to download the project definition for on-device evaluation.While client keys are safe to include, Server and Console keys should always be kept private.

How to add the scope

New SDK Keys
Existing SDK Keys

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

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)")
    }
}

It is possible to configure the SDK to use cached values if they are newer than the local file. This can be useful if you ship your app with a local file, but would like it to only be used for the first session. In the following example, the SDK will only use initialSpecs if there is no cache or if the cache is older than initialSpecs.

let options = StatsigOptions()
options.useNewerCacheValuesOverProvidedValues = true

client.initializeSync(
  "client-sdk-key", 
  initialSpecs: specs,
  options: options
)

You can get a copy of your current specs data by visiting: https://api.statsigcdn.com/v1/download_config_specs/client-{YOUR_SDK_KEY}.json

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

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 a 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)

Code Examples

Working sample apps are available in the repository:

Swift & Objective C Examples

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. Once the user logs in or has an update/changed, make sure to call updateUser with the updated userID and/or any other updated user attributes:

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

Unlike precomputed evaluation SDKs, the on-device evaluation SDK does not have an `updateUser` method since it evaluates gates/configs/experiments in real-time for any user object you pass in.

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

String

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.

Lifecycle & Advanced Usage

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 pass an instance of LocalOverrideAdapter to the SDK via the StatsigOptions object.

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))")
}

FAQs

How do I run experiments for logged out users?

See the guide on device level experiments.

SDK Quickstarts

SDK Concepts

Client SDKs

Server SDKs

AI SDKs

More SDK Methods

Console API Reference

Statsig CLI

HTTP API Reference

Pros

Cons

Set Up the SDK

Working with the SDK

Checking a Feature Flag/Gate

Reading a Dynamic Config

Getting a Layer/Experiment

Logging an Event

Code Examples

Statsig User

Private Attributes

Setting a Global User

Statsig Options

Lifecycle & Advanced Usage

Shutting Statsig Down

Post Init Syncing

From Network

From a Local File

Scheduled Polling

Local Overrides

FAQs

Additional Resources

SDK Quickstarts

SDK Concepts

Client SDKs

Server SDKs

AI SDKs

More SDK Methods

Console API Reference

Statsig CLI

HTTP API Reference

​Pros

​Cons

​Set Up the SDK

​Working with the SDK

​Checking a Feature Flag/Gate

​Reading a Dynamic Config

​Getting a Layer/Experiment

​Logging an Event

​Code Examples

​Statsig User

​Private Attributes

​Setting a Global User

​Statsig Options

​Lifecycle & Advanced Usage

​Shutting Statsig Down

​Post Init Syncing

​From Network

​From a Local File

​Scheduled Polling

​Local Overrides

​FAQs

​Additional Resources

Pros

Cons

Set Up the SDK

Working with the SDK

Checking a Feature Flag/Gate

Reading a Dynamic Config

Getting a Layer/Experiment

Logging an Event

Code Examples

Statsig User

Private Attributes

Setting a Global User

Statsig Options

Lifecycle & Advanced Usage

Shutting Statsig Down

Post Init Syncing

From Network

From a Local File

Scheduled Polling

Local Overrides

FAQs

Additional Resources