RAC ViewModel Action after button pressed with textfield char count as button enabled condition

RAC ViewModel Action on button pressed

import Result
import ReactiveCocoa
import ReactiveSwift
import UIKit
import XCPlayground

struct ViewModel {
  
  // do not expose the implementation detail
  private let (codeSignal, codeSink) = Signal<String, NoError>.pipe()
  
  // change mutable to read-only
  // this will not let the changes outside of VM
  // and only through the `setCode` method
  let code: Property<String>
  
  let openAction: Action<String, String, NoError>
  
  init() {
    code = Property(initial: "", then: codeSignal)
    let validCodes = Property(capturing: code.map { $0.characters.count > 4})
    openAction = Action<String, String, NoError>(enabledIf: validCodes, { code -> SignalProducer<String, NoError> in
      return SignalProducer<String, NoError> { observer, _ in
        print("Code \(code) will be sent.")
        observer.send(value: code)
        observer.sendCompleted()
      }
    })
  }
  
  public func setCode(_ code: String) {
    codeSink.send(value: code)
  }
}

// UI Declarations
let textField = UITextField(frame: CGRect(x: 0, y: 0, width: 360, height: 44))
textField.textColor = .white
textField.text = "P2525"

let button = UIButton(frame: CGRect(x: 0, y: 50, width: 360, height: 44))
button.setTitle("Open", for: .normal)

// Bindings
let viewModel = ViewModel()

// add the `setCode(_:)` function as
// the observer to code text field changes
textField.reactive.continuousTextValues
  .skipNil()
  .observeValues(viewModel.setCode)

// When button is pressed, trigger viewModel action with the property value
button.reactive.pressed = CocoaAction(viewModel.openAction, { _ in
  return viewModel.code.value
})

// bind button's isEnabled to action's isEnabled and action's executing
button.reactive.isEnabled <~ Signal.merge(viewModel.openAction.isEnabled.signal, viewModel.openAction.isExecuting.signal)

// Let's assume the user types and then presses the button, for playground use.
textField.sendActions(for: .allEditingEvents)
button.sendActions(for: .touchUpInside)

Revisions have been made thanks to @eimantas and @sharplet, slack archive for better reference.