ff4k

0.3.0indexed

Feature-flagging toolkit with type-safe properties, DSL configuration, serialization support, custom stores, auto-create behavior, conditional ifEnabled helpers, group management, and extensible property retrieval.

AndroidJVMNative·yonatankarp/ff4k

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FF4K - Feature Flags for Kotlin

Code Quality

FF4K is a Kotlin Multiplatform (KMP) implementation of the popular FF4J (Feature Flipping for Java) library. It brings robust feature flagging capabilities to the Kotlin ecosystem, supporting multiplatform projects.

Features

Kotlin Multiplatform: Designed to work across different platforms supported by Kotlin.
Type-safe Properties: Strongly typed property definitions (String, Int, Boolean, etc.).
Serialization Support: Built-in support for kotlinx.serialization.

Usage

1. Initialization & Configuration

Use the ff4k DSL to configure the library. This allows you to define features and properties in a structured, type-safe way.

import com.yonatankarp.ff4k.dsl.core.ff4k

val ff4k = ff4k {
    // Define features
    features {
        feature("dark-mode") {
            isEnabled = true
            description = "Enable dark mode theme"
            group = 
        }

        feature() {
            isEnabled = 
            permissions(, )
        }
    }

    
    properties {
        property() {
            value = 
            description = 
            readOnly = 
        }

        property() {
            value = 
        }
    }
}

2. Custom Stores & Auto-Create

You can configure storage backends and behavior via the ff4k function arguments.

val ff4k = ff4k(
    autoCreate = true, // Auto-create missing features as disabled
    featureStore = InMemoryFeatureStore(), // Default
    propertyStore = InMemoryPropertyStore() // Default
) {
    // ... configuration block
}

3. Checking Feature Flags

Use the idiomatic ifEnabled and ifEnabledOrElse functions for cleaner conditional logic.

// Execute a block if the feature is enabled
ff4k.ifEnabled("dark-mode") {
    enableDarkMode()
}

// Execute one block if enabled, another if disabled
ff4k.ifEnabledOrElse("dark-mode",
    enabled = { enableDarkMode() },
    disabled = { enableLightMode() }
)

4. Retrieving Properties

Access properties safely with type conversion.

// Retrieve property object and access its value
val retries: Int? = ff4k.property<Int>("max-retries")?.value
val apiUrl: String? = ff4k.property<String>("api-url")?.value

5. Managing Groups

Enable or disable entire groups of features.

// Enable all features in the 'ui-experiments' group
ff4k.enableGroup("ui-experiments")

// Disable all features in the 'ui-experiments' group
ff4k.disableGroup("ui-experiments")