Vexillum (/vɛkˈsɪləm/) was a flag-like object used as a military standard by units in the Ancient Roman army.
Vexillum is a Kotlin package for managing feature flags.

Setup

Gradle

implementation "io.github.pavelannin:vexillum:0.1.1"

Quickstart

1. Feature flags spaces

// Space for feature flags
object LocalFeatureFlags {

    // Static type cannot be changed after compilation
    val isQrScannerEnabled = FeatureToggle.Static(
        isEnabled = true, // Required
        key = "qr_scanner", // Optional, unique to all space (by default, the UUID is used)
        name = "Qr Scanner", // Optional, human readable name
        description = "Enable the ability to scan QR codes", // Optional, human readable description,
        payload = Unit // Optional
    )

    // Dynamic type change in runtime
    val isAuthEnabled = FeatureToggle.Dynamic(
        defaultEnabled = true, // Required, initial value
        key = "auth", // Optional, unique to all space (by default, the UUID is used)
        name = "Auth", // Optional, human readable name
        description = "Enable user authorization", // Optional, human readable description,
        defaultPayload = Unit // Optional, initial payload value
    )
}

2. Creating providers for dynamic feature flags

class ExampleService {
    suspend fun fetchFeatureFlags(): FeatureFlagsResponse = TODO()
    data class FeatureFlagsResponse(val auth: Boolean)
}

fun exampleProviderFeatureFlags(exampleService: ExampleService) = Vexillum.Provider {
    flow {
        val response = exampleService.fetchFeatureFlags()
        emit(
            setOf(
                Vexillum.Provider.Result(
                    feature = LocalFeatureFlags.isAuthEnabled,
                    newEnabled = response.auth,
                    newPayload = Unit
                ),
                // other feature flags
            )
        )
    }
}

3. Creating Vexillum

val vexillum = Vexillum(
    exampleProviderFeatureFlags(ExampleService()),
    // supports multi providers
)

4. Usage

// Only for static
vexillum.isEnabled(LocalFeatureFlags.isQrScannerEnabled) // Boolean
vexillum.payload(LocalFeatureFlags.isQrScannerEnabled) // Payload generic type

// Only for dynamic
vexillum.observeEnabled(LocalFeatureFlags.isAuthEnabled) // StateFlow<Boolean>
vexillum.observePayload(LocalFeatureFlags.isAuthEnabled) // StateFlow<Payload> generic type