Finite State Machine

A simple Finite State Machine implementation for Roblox development written using roblox-ts.

Installation

roblox-ts

Simply install to your roblox-ts project as follows:

npm i @rbxts/finite-state-machine

Wally

Wally users can install this package by adding the following line to their Wally.toml under [dependencies]:

FiniteStateMachine = "bytebit/[email protected]"

Then just run wally install.

From model file

Model files are uploaded to every release as .rbxmx files. You can download the file from the Releases page and load it into your project however you see fit.

From model asset

New versions of the asset are uploaded with every release. The asset can be added to your Roblox Inventory and then inserted into your Place via Toolbox by getting it here.

Documentation

IReadonlyFiniteStateMachine interface

This interface is meant to be used when there is a consumer that merely cares about the state of the machine but not to do anything to affect that state.

It requires two generic inputs - a StateType and an EventType. Both must simply fit the type defined.

stateChanged Signal

readonly stateChanged: IReadOnlySignal<(newState: StateType, oldState: StateType, event: EventType) => void>;

Fired when the current state is changed by an event.

getCurrentState Method

getCurrentState(): StateType;

Used to get the current state of the machine.

FiniteStateMachine class

Implements everything from IReadonlyFiniteStateMachine.

This is the root of this package.

Construction

In order to construct a FiniteStateMachine instance, you will need to define your states, events, and the transition relationships between them. The transition relationships are represented using a nested tuple of [[fromState, event], toState].

Take this on/off switch as an example:

type StateType = "On" | "Off";
type EventType = "Toggle";
const stateTransitions = new Map<[StateType, EventType], StateType>([
	[["Off", "Toggle"], "On"],
	[["On", "Toggle"], "Off"]
]);
const fsm = FiniteStateMachine.create("Off", stateTransitions);

destroy Method

destroy(): void

This method is used to destroy an instance. That instance will throw exceptions if any other methods are used after this is invoked.

handleEvent Method

handleEvent(event: EventType): void

This method is used to effect a state transition though an event. If the given event has a valid state to transition to from the current state as per the state transitions at the time of the instance's construction, the state will be changed accordingly; otherwise, an error will be raised.

Example using the on/off switch from above:

function toggleSwitch() {
	fsm.handleEvent("Toggle");
}