KStateMachine

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KStateMachine is a Kotlin DSL library for creating state machines and statecharts.

Overview

Integration features are:

• Kotlin DSL syntax. Declarative and clear state machine structure. Using without DSL is also possible.
• Kotlin Coroutines support. Call suspendable functions within the library. You can fully use KStateMachine without Kotlin Coroutines dependency if necessary.
• Kotlin Multiplatform support.
• Zero dependency. It is written in pure Kotlin, it does not depend on any third party libraries or Android SDK.

State management features:

• Event based - transitions are performed by processing incoming events
• Reactive - listen for machine, states, state groups and transitions
• Guarded and Conditional transitions - dynamic target state which is calculated in a moment of event processing depending on application business logic
• Nested states - build hierarchical state machines ( statecharts) with cross-level transitions support
• Composed (nested) state machines. Use state machines as atomic child states
• Pseudo states for additional logic in machine behaviour
• Typesafe transitions - pass data in typesafe way from event to state
• Parallel states - avoid a combinatorial explosion of states
• Undo transitions - navigate back to previous state
• Optional argument passing for events and transitions
• Export state machine structure to PlantUML
• Logging - useful for debugging
• Testable - run state machine from specified state
• Well tested - all features are covered by tests

Quick start sample

Finishing traffic light

stateDiagram-v2
    direction LR
    [*] --> GreenState
    GreenState --> YellowState : SwitchEvent
    YellowState --> RedState : SwitchEvent
    RedState --> [*]

object SwitchEvent : Event

sealed class States : DefaultState() {
    object GreenState : States()
    object YellowState : States()
    object RedState : States(), FinalState // Machine finishes when enters final state
}

fun main() = runBlocking {
    // Create state machine and configure its states in a setup block
    val machine = createStateMachine(this) {
        addInitialState(GreenState) {
            // Add state listeners
            onEntry { println("Enter green") }
            onExit { println("Exit green") }

            // Setup transition
            transition<SwitchEvent> {
                targetState = YellowState
                // Add transition listener
                onTriggered { println("Transition triggered") }
            }
        }

        addState(YellowState) {
            transition<SwitchEvent>(targetState = RedState)
        }

        addFinalState(RedState)

        onFinished { println("Finished") }
    }

    // Now we can process events
    machine.processEvent(SwitchEvent)
    machine.processEvent(SwitchEvent)
}

Samples

• Simple Android 2D shooter game sample

  The library itself does not depend on Android.

• Transition on FinishedEvent sample

• FinishedEvent using with DataState sample

• Undo transition sample

• PlantUML nested states export sample

• Inherit transitions by grouping states sample

• Minimal sealed classes sample

• Usage without Kotlin Coroutines sample

• Minimal syntax sample

• Guarded transition sample

• Cross-level transition sample

• Typesafe transition sample

• Complex syntax sample shows many syntax variants and library possibilities, so it looks messy

Install

KStateMachine is available on Maven Central and JitPack repositories.

The library consists of 2 components:

• kstatemachine - (mandatory) state machine implementation (depends only on Kotlin Standard library)
• kstatemachine-coroutines - (optional) add-ons for working with coroutines (depends on Kotlin Coroutines library)

Please note that starting from v0.22.0 the library switched to Kotlin Multiplatform and artifact naming has changed.

Maven Central

Add dependencies:

// kotlin
dependencies {
    // multiplatform artifacts (starting from 0.22.0)
    implementation("io.github.nsk90:kstatemachine:<Tag>")
    implementation("io.github.nsk90:kstatemachine-coroutines:<Tag>")
    // or JVM/Android artifacts (starting from 0.22.0)
    implementation("io.github.nsk90:kstatemachine-jvm:<Tag>")
    implementation("io.github.nsk90:kstatemachine-coroutines-jvm:<Tag>")
    // or iOS artifacts (starting from 0.22.1)
    implementation("io.github.nsk90:kstatemachine-iosarm64:<Tag>")
    implementation("io.github.nsk90:kstatemachine-coroutines-iosarm64:<Tag>")

    implementation("io.github.nsk90:kstatemachine-iosx64:<Tag>")
    implementation("io.github.nsk90:kstatemachine-coroutines-iosx64:<Tag>")

    implementation("io.github.nsk90:kstatemachine-iossimulatorarm64:<Tag>")
    implementation("io.github.nsk90:kstatemachine-coroutines-iossimulatorarm64:<Tag>")
}

// groovy
dependencies {
    // multiplatform artifacts
    implementation 'io.github.nsk90:kstatemachine:<Tag>'
    implementation 'io.github.nsk90:kstatemachine-coroutines:<Tag>' // optional
    // etc..
}

Where <Tag> is a library version.

You can see official docs about dependencies on multiplatform libraries

JitPack (deprecated)

Currently, JitPack does not support Kotlin multiplatform artifacts. So versions starting from 0.22.0 are not available there, use Maven Central instead.

Add the JitPack repository to your build file. Add it in your root build.gradle at the end of repositories:

// kotlin
repositories {
    //  ...
    maven { url = uri("https://jitpack.io") }
}

// groovy
allprojects {
    repositories {
        //  ...
        maven { url 'https://jitpack.io' }
    }
}

Add dependencies:

// kotlin
dependencies {
    implementation("com.github.nsk90:kstatemachine:<Tag>")
    // note that group is different in second artifact, long group name also works for first artifact but not vise versa
    // it is some strange JitPack behaviour
    implementation("com.github.nsk90.kstatemachine:kstatemachine-coroutines:<Tag>") // optional
}

// groovy
dependencies {
    implementation 'com.github.nsk90:kstatemachine:<Tag>'
    // note that group is different in second artifact, long group name also works for first artifact but not vise versa
    // it is some strange JitPack behaviour
    implementation 'com.github.nsk90.kstatemachine:kstatemachine-coroutines:<Tag>' // optional
}

Where <Tag> is a library version.

Build

Run ./gradlew build or build with Intellij IDEA.

To run tests from IDE download official Kotest plugin.

License

Licensed under permissive Boost Software License

Thanks to supporters