Elm

This is Elm architecture for Swift.

Interface

static func update(for message: Message, model: inout Model) -> [Command]
static func view(for model: Model) -> View

Example

Let's build a counter:

Functional core

• Module:

  struct Counter: Module {
  
      enum Message {
          case userDidTapIncrementButton
          case userDidTapDecrementButton
      }
  
      struct Model: Initable {
          var count = 0
      }
  
      struct View {
          let title = "Counter"
          let count: String
          let incrementButton = Button(
              title: "Increment",
              callback: .userDidTapIncrementButton
          )
          let decrementButton = Button(
              title: "Decrement",
              callback: .userDidTapDecrementButton
          )
          struct Button {
              let title: String
              let callback: Message
          }
      }
  
      enum Command {}
  
      static func update(for message: Message, model: inout Model) -> [Command] {
          switch message {
          case .userDidTapIncrementButton:
              model.count += 1
          case .userDidTapDecrementButton:
              model.count -= 1
          }
          return []
      }
  
      static func view(for model: Model) -> View {
          let count = String(model.count)
          return View(count: count)
      }
      
  }

• Program:

  let counter = Counter.makeProgram()

Imperative shell

• Storyboard:

• View controller:

  class CounterViewController: UIViewController, Subscriber {
  
      typealias View = Counter.View
      typealias Command = Counter.Command
  
      @IBOutlet var countLabel: UILabel?
  
      @IBOutlet var incrementButton: UIBarButtonItem?
      @IBOutlet var decrementButton: UIBarButtonItem?
  
      override func viewDidLoad() {
          super.viewDidLoad()
          counter.subscribe(self)
      }
  
      func update(presenting view: View) {
          title = view.title
          countLabel?.text = view.count
          incrementButton?.title = view.incrementButton.title
          decrementButton?.title = view.decrementButton.title
      }
  
      func update(performing command: Command) {}
  
      @IBAction func userDidTapIncrementButton() {
          counter.dispatch(counter.view.incrementButton.callback)
      }
  
      @IBAction func userDidTapDecrementButton() {
          counter.dispatch(counter.view.decrementButton.callback)
      }
  
  }