Finite

Finite is a simple, pure Swift finite state machine. Only exlicitly allowed transitions between states are allowed, otherwise an error will be thrown.

Finite	Swift
2.0.0	2.2 and 3.0 Beta
3.x.x	3.0 and 4.0
4.x.x	5.0

Installation

Finite has no external dependencies and supports Swift Package Manager, Carthage and CocoaPods.

Swift Package Manager

import PackageDescription

let package = Package(
    name: "YourPackage",
    dependencies: [
        .package(url: "https://github.com/vknabel/Finite.git", from: "4.0.0")
    ],
    targets: [
        .target(name: "YourTarget", dependencies: ["Finite"]),
    ]
)

Carthage

github "vknabel/Finite"

CocoaPods

source 'https://github.com/CocoaPods/Specs.git'
use_frameworks!

pod 'Finite', '~> 4.0.0'

Introduction

It operates on a given type, where each value represents an internal state of the machine. A StateMachine is defined by providing all allowed state transitions.

enum Test: Int {
    case saving, fetching, deleting
    case ready, fail
}

var machine = StateMachine<Test>(initial: .ready) { c in
    c.allow(from: [.saving, .fetching, .deleting], to: [.ready, .fail])
    c.allow(from: .ready, to: [.saving, .fetching, .deleting])
}

It is possible to provide callbacks, that will be called once certain transitions will happen.

machine.onTransitions {
    println("Successfully triggered transition!")
}
machine.onTransitions(from: .ready) {
    println("From Ready: show activity indicator")
}
machine.onTransitions(to: .ready) {
    println("To Ready: hide activity indicator")
}
machine.onTransitions(to: .saving) {
    println("To: save")
}

let subscription = machine.subscribeTransitions(to: .saving) {
    println("Only triggered as long as you keep `subscription`")
}

Once the StateMachine has been set up, you may trigger all transitions you have declared above.

try machine.transition(to: .saving) {
    println("Triggered: save")
}

// this will throw TransitionError<Test>.denied(from: .saving, to: .fetching)
try machine.transition(to: .fetching)

Author

Valentin Knabel, dev@vknabel.com

Special thanks to @snofla for allowing to export state machines to graphviz.

License

Finite is available under the MIT license.