FF4K - Feature Flags for Kotlin¶

FF4K is a Kotlin Multiplatform port of the ideas behind FF4J: feature flags, flipping strategies and typed properties behind a small, coroutine-first API.

Key Features¶

Small API: one FF4k entry point, plain data classes, suspend functions.
Flipping Strategies: gradual rollouts, user targeting and time windows with built-in strategies, composable with and, or and !.
Typed Properties: Property<T> values for String, Int, Long, Double, Boolean, Instant, LocalDate and LocalDateTime.
JSON configuration: load features and properties from a file with kotlinx.serialization.
Pluggable stores: in-memory and SQLite out of the box, custom stores verified by contract tests.

Alpha. FF4K is pre-1.0. Public APIs, the JSON format and store schemas change between releases without a deprecation cycle.

Installation¶

Use the BOM so all FF4K modules share one version:

repositories {
    mavenCentral()
}

dependencies {
    implementation(platform("com.yonatankarp:ff4k-bom:<version>"))
    implementation("com.yonatankarp:ff4k-core")
}

Or pin each module: implementation("com.yonatankarp:ff4k-core:<version>").

Quick Start¶

suspend fun main() {
    val ff4k = FF4k()
    ff4k.features.put(Feature("dark-mode", enabled = true))

    if (ff4k.check("dark-mode")) {
        // ...
    }
}

Continue with the Basics guide.

License¶

Apache License 2.0.