Playing around w/ protocols in Swift

Protocolling in Swift

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

import UIKit

protocol HomeViewControllerProtocol: class {
    func render()
}

class HomeViewController_1: UIViewController, HomeViewControllerProtocol {
    func render() { print("1") }
}
class HomeViewController_2: UIViewController, HomeViewControllerProtocol {
    func render() { print("2") }
}

typealias HomeViewController = UIViewController & HomeViewControllerProtocol // 👈👈👈

class Factory {
    func home() -> HomeViewController {
        return HomeViewController_1()
    }
}

let obj = Factory().home()
obj.render() //this is ok
obj.title = "sadfasfa" //this is also ok

// or via extension

protocol P {
    func title_ext() -> String?
}

extension UIViewController: P {
    func title_ext() -> String? {
        return title
    }
    
    func somethingElse() -> String? {
        return title
    }
}

class HomeViewController_3: UIViewController { }
class HomeViewController_4: UIViewController { }

typealias ControllerAndP = UIViewController & P // 👈👈👈

class Factory2 {
    func homeVC() -> UIViewController {
        return HomeViewController_3()
    }
    func homeVCAndP() -> ControllerAndP {
        return HomeViewController_3()
    }
}

let obj2 = Factory2().homeVC()
obj2.title_ext() //this is ok
obj2.title = "sadfasfa" //this is also ok
obj2.somethingElse()

let obj3 = Factory2().homeVCAndP()
obj3.title_ext() //this is ok
obj3.title = "sadfasfa" //this is also ok
obj3.somethingElse()

// Error management

public protocol DialogPresentation {
    func showError(title: String, message: String)
}

extension UIView: DialogPresentation {
    func showError(title: String, message: String) {
        // ...
    }
}

extension UIViewController: DialogPresentation {
    func showError(title: String, message: String) {
        // ...
    }
}

// cannot do directly an extension of DialogPresentation,
// need to use `Self: DialogPresentation`, so that the extension applies to UIView and UIViewController.
// It's tricky at first.
// This means I need to create an extra protocol (ShowError) that will be extended with such clause
// also need to create the extensions for the classes that I want the common implementation

public protocol ShowError {
    func show(error: NSError)
}

extension UIView: ShowError { }
extension UIViewController: ShowError { }

extension ShowError where Self: DialogPresentation {
    public func show(error: NSError) {
        // ...
        self.showError(title: title, message: message)
    }
    
}