SwiftyStateSignals

SwiftyStateSignals is a simple finite state machine framework inspired by StateSignals and built on ReactiveCocoa signals.

Installation

SwiftyStateSignals can be imported just like any framework, but is easy to use with Carthage. Just add the following to your Cartfile:

github "simonyangme/SwiftyStateSignals"

Example

Begin by defining enums for states:

enum TurnstileState {
    case Locked, Unlocked
}

and events:

enum TurnstileEvent {
    case Coin, Push
}

Then create a transition dictionary with the desired transitions and create the state machine:

let transitions = TransitionDictionary<TurnstileState, TurnstileEvent>()
transitions.mapEvent(.Coin, fromState: .Locked, toState: .Unlocked)
transitions.mapEvent(.Push, fromState: .Unlocked, toState: .Locked)

let machine = SignalMachine(transitionDictionary: transitions, withInitialState: .Locked)

We can observe for changes by subscribing to any of the signals that the state machine vends. For example:

machine.allTransitions().observe(next: { transition in
    NSLog("Observed an event")
    // Do stuff here
})
	
	machine.transitionFaults().observe(next: { transition in
    NSLog("Invalid event; no transition occurred")
    // Do other stuff here
})

Transitions are defined as such:

struct Transition<State, Event> {
    let fromState: State
    let toState: State?
    let event: Event
}

Transitions are Printable, but will only display Enum Value for your states and events if they are not. To pretty print transitions, make your enums Printable, like so:

enum TurnstileState: Printable {
	case Locked, Unlocked
	var description: String {
		get {
			switch self {
			case .Locked:
				return "Locked"
			case .Unlocked:
				return "Unlocked"
			}
		}
	}
}

enum TurnstileEvent: Printable {
	case Coin, Push
	var description: String {
		get {
			switch self {
			case .Coin:
				return "Coin"
			case .Push:
				return "Push"
			}
		}
	}
}

machine.allTransitions().observe(next: { t in
    NSLog("\(t)")
})
machine.inputEvent(.Coin)

will print:

Transition: Locked -> Optional(Unlocked), Event: Coin