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A Kotlin DSL for finite state machine.
StateMachine is used in Scarlet
In this example, we create a StateMachine from the following state diagram.
Define states, event, and side effects:
sealed class State {
object Solid : State()
object Liquid : State()
object Gas : State()
}
sealed class Event {
object OnMelted : Event()
object OnFroze : Event()
object OnVaporized : Event()
object OnCondensed : Event()
}
sealed class SideEffect {
object LogMelted : SideEffect()
object LogFrozen : SideEffect()
object LogVaporized : SideEffect()
object LogCondensed : SideEffect()
}Declare state transitions:
val stateMachine = StateMachine.create<State, Event, SideEffect> {
initialState(State.Solid)
state<State.Solid> {
on<Event.OnMelted> {
transitionTo(State.Liquid, SideEffect.LogMelted)
}
}
state<State.Liquid> {
on<Event.OnFroze> {
transitionTo(State.Solid, SideEffect.LogFrozen)
}
on<Event.OnVaporized> {
transitionTo(State.Gas, SideEffect.LogVaporized)
}
}
state<State.Gas> {
on<Event.OnCondensed> {
transitionTo(State.Liquid, SideEffect.LogCondensed)
}
}
onTransition {
val validTransition = it as? StateMachine.Transition.Valid ?: return@onTransition
when (validTransition.sideEffect) {
SideEffect.LogMelted -> logger.log(ON_MELTED_MESSAGE)
SideEffect.LogFrozen -> logger.log(ON_FROZEN_MESSAGE)
SideEffect.LogVaporized -> logger.log(ON_VAPORIZED_MESSAGE)
SideEffect.LogCondensed -> logger.log(ON_CONDENSED_MESSAGE)
}
}
}Perform state transitions:
assertThat(stateMachine.state).isEqualTo(Solid)
// When
val transition = stateMachine.transition(OnMelted)
// Then
assertThat(stateMachine.state).isEqualTo(Liquid)
assertThat(transition).isEqualTo(
StateMachine.Transition.Valid(Solid, OnMelted, Liquid, LogMelted)
)
then(logger).should().log(ON_MELTED_MESSAGE)Thanks to @nvinayshetty, you can visualize your state machines right in the IDE using the State Arts Intellij plugin.
StateMachine is available in Maven Central.
Snapshots of the development version are available in Sonatype's snapshots repository.
<dependency>
<groupId>com.tinder.statemachine</groupId>
<artifactId>statemachine</artifactId>
<version>0.2.0</version>
</dependency>implementation 'com.tinder.statemachine:statemachine:0.2.0'Copyright (c) 2018, Match Group, LLC
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