A/B and Feature Flags

Easily configure and retrieve A/B and feature flag configuration.

Why Does This Exist?

I couldn't find a solution that fit my needs. I needed something that was dead simple to configure and use.

What Is It For?

I needed a way to continue development on half-baked features while still deploying features or fixes that are complete.

I also needed an easy way to A/B[/C] test using Swift enum types rather than primitive types (Bool). While the API supports multi-variant values it is built for the most common use-case which is to determine if something is either off or on (Bool).

How It Works

As said before I need to support two different types of flags:

• Feature flags: Flags which prevent features from being visible in a prod/qa/etc environment while the feature is still being worked on
• A/B[/C] flags: Flags that turn certain features on or off to determine fitness of a given feature

In some cases it may be necessary to feature flag A/B flag development work.

Initialization & Configuration

The flags must first be registered before they can be used.

// Initialize the flags manager which will return configured values for the production environment.
let flags = Flags(environment: .prod)

// Register the flags
flags.register(flags: [
    Flag<ButtonColor>(id: .buttonColor, key: "button_color", default: .default, available: [.all], mapper: ButtonColor.mapper),
    Flag<Bool>(id: .enableFlyoutMenu, default: false, available: [.dev, .qa])
])

In this example we have a multi-variant A/B flag FlagID.buttonColor which is of type ButtonColor. It is available in .all environments. Simply, this means we will be provided with the value of Flag.value if it has been set by the server config.

The other flag is a feature flag called FlagID.enableFlyoutMenu. It is available only in the development and QA environments. This means that if this flag's configuration value is read in production it will always return the default Flag.value of false.

Retrieving Flag Values

The most common use case is to determine if a flag is enabled. This can be done by calling Flags.isEnabled(for:).

// Get a boolean value (the most common case) for our flag
print("Is the flyout menu enabled? \(flags.isEnabled(for: .enableFlyoutMenu) ? "Yes" : "No").")
// prints: `No`, because we are configured for production and this flag isn't available in production

Let's get our multi-variant value. Because the server has not yet configured our flag's value, it will return the default value.

// Get the multi-variant button color value
var buttonColor = flags.value(for: .buttonColor, ButtonColor.self)
print("The button color is: \(buttonColor.rawValue)")
// prints: `default`, as the server configuration hasn't been set yet!

Now let's simulate setting the server config value for FlagID.buttonColor and getting the value again.

// Simulate setting the flag value from the server
flags.setValue(key: "button_color", value: "red")

// Get the multi-variant button color value (again)
buttonColor = flags.value(for: .buttonColor, ButtonColor.self)
print("The button color is: \(buttonColor.rawValue)")
// prints: `red`, as the `Flag.value` has been set by the server!

License

MIT