ProtocolComposition+DependencyInjection.swift

//: A UIKit based Playground for presenting user interface
  
import UIKit
import PlaygroundSupport

protocol GreetService {
  func greeting() -> String
}

class Greeter: GreetService{
  func greeting() -> String {
    return "Hello, World!"
  }
}

protocol StyleService {
  func textColor() -> UIColor
  func backgroundColor() -> UIColor
}

class DefaultStyle: StyleService {
  func textColor() -> UIColor {
    return .green
  }

  func backgroundColor() -> UIColor {
    return .blue
  }
}

protocol HasStyleService {
  var styleService: StyleService { get }
}

protocol HasGreetService {
  var greetService: GreetService { get }
}

struct Dependencies: HasStyleService, HasGreetService {
  var styleService: StyleService
  var greetService: GreetService
}

class MyViewController : UIViewController {
  typealias Dependencies = HasGreetService & HasStyleService
  let dependencies: Dependencies
  init(dependencies: Dependencies) {
    self.dependencies = dependencies
    super.init(nibName: nil, bundle: nil)
  }

  @available(*, unavailable)
  required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }


  override func loadView() {
    let view = UIView()
    view.backgroundColor = dependencies.styleService.backgroundColor()

    let label = UILabel()
    label.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
    label.text = dependencies.greetService.greeting()
    label.textColor = dependencies.styleService.textColor()

    view.addSubview(label)
    self.view = view
  }
}

let AppDepenencies = Dependencies(styleService: DefaultStyle(), greetService: Greeter())
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController(dependencies: AppDepenencies)