Unidirectional State Management Architecture for Swift - Inspired by Vuex and Flux

Introduction

VueFlux is the architecture to manage state with unidirectional data flow for Swift, inspired by Vuex and Flux.

It serves multi store, so that all ViewControllers have designated stores, with rules ensuring that the states can only be mutated in a predictable fashion.

The stores also can receives an action dispatched globally.
That makes ViewControllers be freed from dependencies among them. And, a shared state in an application is also supported by a shared instance of the store.

Although VueFlux makes your projects more productive and codes more readable, it also comes with the cost of more concepts and boilerplates.
If your project is small-scale, you will most likely be fine without VueFlux.
However, as the scale of your project becomes larger, VueFlux will be the best choice to handle the complicated data flow.

VueFlux is receives state changes by efficient reactive system. VueFluxReactive is µ reactive framework compatible with this architecture.
Arbitrary third party reactive frameworks (e.g. RxSwift, ReactiveSwift, etc) can also be used with VueFlux.

About VueFlux

VueFlux makes a unidirectional and predictable flow by explicitly dividing the roles making up the ViewController. It's constituted of following core concepts.
State changes are observed by the ViewController using the reactive system.
Sample code uses VueFluxReactive which will be described later.
You can see example implementation here.

• State
• Actions
• Mutations
• Computed
• Store

State

This is the protocol that only just for constraining the type of Action and Mutations, represents the state managed by the Store.
Implement some properties of the state, and keeps them readonly by fileprivate access control, like below.
Will be mutated only by Mutations, and the properties will be published only by Computed.

final class CounterState: State {
    typealias Action = CounterAction
    typealias Mutations = CounterMutations

    fileprivate let count = Variable(0)
}

Actions

This is the proxy for functions of dispatching Action.
They can have arbitrary operations asynchronous such as request to backend API.
The type of Action dispatched from Actions' function is determined by State.

enum CounterAction {
    case increment, decrement
}

extension Actions where State == CounterState {
    func increment() {
        dispatch(action: .increment)
    }

    func decrement() {
        dispatch(action: .decrement)
    }
}

Mutations

This is the protocol that represents commit function that mutate the state.
Be able to change the fileprivate properties of the state by implementing it in the same file.
The only way to actually change State in a Store is committing an Action via Mutations.
Changes of State must be done synchronously.

struct CounterMutations: Mutations {
    func commit(action: CounterAction, state: CounterState) {
        switch action {
        case .increment:
            state.count.value += 1

        case .decrement:
            state.count.value -= 1
        }
    }
}

Computed

This is the proxy for publishing read-only properties of State.
Be able to access and publish the fileprivate properties of state by implementing it in the same file.
Properties of State in the Store can only be accessed via this.

extension Computed where State == CounterState {
    var countTextValues: Signal<String> {
        return state.count.signal.map { String($0) }
    }
}

Store

The Store manages the state, and also can be manage shared state in an application by shared store instance.
Computed and Actions can only be accessed via this. Changing the state is the same as well.
An Action dispatched from the actions of the instance member is mutates only the designated store's state.
On the other hand, an Action dispatched from the actions of the static member will mutates all the states managed in the stores which have same generic type of State in common.
Store implementation in a ViewController is like as follows:

final class CounterViewController: UIViewController {
    @IBOutlet private weak var counterLabel: UILabel!

    private let store = Store<CounterState>(state: .init(), mutations: .init(), executor: .queue(.global()))

    override func viewDidLoad() {
        super.viewDidLoad()

        store.computed.countTextValues.bind(to: counterLabel, \.text)
    }

    @IBAction func incrementButtonTapped(sender: UIButton) {
        store.actions.increment()  // Store<CounterState>.actions.increment()
    }

    @IBAction func decrementButtonTapped(sender: UIButton) {
        store.actions.decrement()  // Store<CounterState>.actions.decrement()
    }
}

About VueFluxReactive

VueFluxReactive is a μ reactive system for observing state changes.
It was made for replacing the existing reactive framework that takes high learning and introduction costs though high-powered such as RxSwift and ReactiveSwift.
But, of course, VueFlux can be used with those framework because VueFluxReactive is separated.
VueFluxReactive is constituted of following primitives.

• Variable
• Constant
• Sink
• Signal

Sink

This type has a way of generating Signal.
One can send values into a sink and receives it by observing generated signal.
Signals generated from Sink does not hold the latest value.
Practically, it's used to send commands (such as presents another ViewController) from State to ViewController.
Can't deliver values recursively.

let sink = Sink<Int>()
let signal = sink.signal

signal.observe { print($0) }

sink.send(value: 100)

// prints "100"

Signal

A push-driven stream that sends value changes over time.
Values will be sent to all registered observers at the same time.
All of values changes are made via this primitive.

let sink = Sink<Int>()
let signal = sink.signal

signal.observe { print("1: \($0)") }
signal.observe { print($2: \($0)") }

sink.send(value: 100)
sink.send(value: 200)

// prints "1: 100"
// prints "2: 100"
// prints "1: 200"
// prints "2: 200"

Variable

Variable represents a thread-safe mutable value that allows observation of its changes via signal generated from it.
The signal forwards the latest value when observing starts. All value changes are delivers on after that.
Can't deliver values recursively.

let variable = Variable(0)

variable.signal.observe { print($0) }

variable.value = 1

print(variable.value)

variable.signal.observe { print($0) }

/// prints "0"
/// prints "1"
/// prints "1"
/// prints "1"

Constant

This is a kind of wrapper to making Variable read-only.
Constant generated from Variable reflects the changes of its Variable.
Just like Variable, the latest value and value changes are forwarded via signal. But Constant is not allowed to be changed directly.

let variable = Variable(0)
let constant = variable.constant

constant.signal.observe { print($0) }

variable.value = 1

print(constant.value)

constant.signal.observe { print($0) }

/// prints "0"
/// prints "1"
/// prints "1"
/// prints "1"

Advanced Usage

Executor

Executor determines the execution context of function such as execute on main thread, on a global queue and so on.
Some contexts are built in default.

• immediate
  Executes function immediately and synchronously.

• mainThread
  Executes immediately and synchronously if execution thread is main thread. Otherwise enqueue to main-queue.

• queue(_ dispatchQueue: DispatchQueue)
  All functions are enqueued to given dispatch queue.

In the following case, the store commits actions to mutations on global queue.

let store = Store<CounterState>(state: .init(), mutations: .init(), executor: .queue(.global()))

If you observe like below, the observer function is executed on global background queue.

store.computed.valueSignal
    .observe(on: .queue(.global(qos: .background)))
    .observe { value in
        // Executed on global background queue
}

Signal Operators

VueFluxReactive restricts functional approach AMAP.
However, includes minimum operators for convenience.
These operators transform a signal into a new sinal generated in the operators, which means the invariance of Signal holds.

map
The map operator is used to transform the values in a signal.

let sink = Sink<Int>()
let signal = sink.signal

signal
    .map { "Value is \($0)" }
    .observe { print($0) }

sink.send(value: 100)
sink.send(value: 200)

// prints "Value is 100"
// prints "Value is 200"

observe(on:)
Forwards all values ​​on context of a given Executor.

let sink = Sink<Int>()
let signal = sink.signal

signal
    .observe(on: .mainThread)
    .observe { print("Value: \($0), isMainThread: \(Thread.isMainThread)") }

DispatchQueue.global().async {
    sink.send(value: 100)    
    sink.send(value: 200)
}

// prints "Value: 100, isMainThread: true"
// prints "Value: 200, isMainThread: true"

Disposable

Disposable represents something that can be disposed, usually unregister a observe that registered to Signal.

let disposable = signal.observe { value in
    // Not executed after disposed.
}

disposable.dispose()

DisposableScope

DisposableScope serves as resource manager of Disposable.
This will terminate all added disposables on deinitialization or disposed.
For example, when the ViewController which has a property of DisposableScope is dismissed, all disposables are terminated.

var disposableScope: DisposableScope? = DisposableScope()

disposableScope += signal.observe { value in
    // Not executed after disposableScope had deinitialized.
}

disposableScope = nil  // Be disposed

Scoped Observing

In observing, you can pass AnyObject as the parameter of duringScopeOf:.
An observer function which is observing the Signal will be dispose when the object is deinitialize.

signal.observe(duringScopeOf: self) { value in
    // Not executed after `self` had deinitialized.
}

Bind

Binding makes target object's value be updated to the latest value received via Signal.
The binding is no longer valid after the target object is deinitialized.
Bindings work on main thread by default.

Closure binding.

text.signal.bind(to: label) { label, text in
    label.text = text
}

Smart KeyPath binding.

text.signal.bind(to: label, \.text)

Binder

extension UIView {
    func setHiddenBinder(duration: TimeInterval) -> Binder<Bool> {
        return Binder(target: self) { view, isHidden in
            UIView.transition(
              with: view,
              duration: duration,
              options: .transitionCrossDissolve,
              animations: { view.isHidden = isHidden }
            )
        }
    }
}

isViewHidden.signal.bind(to: view.setHiddenBinder(duration: 0.3))

Shared Store

You should make a shared instance of Store in order to manages a state shared in application.
Although you may define it as a global variable, an elegant way is overriding the Store and defining a static member shared.

final class CounterStore: Store<CounterState> {
    static let shared = CounterStore()

    private init() {
        super.init(state: .init(), mutations: .init(), executor: .queue(.global()))
    }
}

Global Dispatch

VueFlux can also serve as a global event bus.
If you call a function from actions that is a static member of Store, all the states managed in the stores which have same generic type of State in common are affected.

let store = Store<CounterState>(state: .init(), mutations: .init(), executor: .immediate)

print(store.computed.count.value)

Store<CounterState>.actions.increment()

print(store.computed.count.value)

// prints "0"
// prints "1"

Requirements

• Swift4.1+
• OS X 10.9+
• iOS 9.0+
• watchOS 2.0+
• tvOS 9.0+

Installation

CocoaPods

If use VueFlux with VueFluxReactive, add the following to your Podfile:

use_frameworks!

target 'TargetName' do
  pod 'VueFluxReactive'
end

Or if, use with third-party Reactive framework:

use_frameworks!

target 'TargetName' do
  pod 'VueFlux'
  # And reactive framework you like
end

And run

pod install

Carthage

Add the following to your Cartfile:

github "ra1028/VueFlux"

And run

carthage update

Example Projects

• VueFluxExample-GitHub: Simple example using GitHub user search API.

Contribution

Welcome to fork and submit pull requests.

Before submitting pull request, please ensure you have passed the included tests.
If your pull request including new function, please write test cases for it.

License

VueFlux and VueFluxReactive is released under the MIT License.