protocols promised-land-2

Protocols and the Promised Land

@MicheleTitolo

Swift is shiny! And new!

Swift is not Objective-C

Interop

as? as? as?

as? lies

🚫let vendor = ObjcObject() let items = vendor.giveMeItems() as? [Fruit]

let vendor = ObjcObject() let items = vendor.giveMeItems().map { $0 as Fruit }

@objc spreads like a virus

🚫

@objc protocol SomeProtocol { func someFunc() }

class MyClass: SomeProtocol {}

@objc protocol SomeProtocol { func someFunc() }

@objc class MyClass: NSObject, SomeProtocol {}

Swift > Objc > Swift

Can’t #import “MyApp-Swift.h” in header

Can’t conform, can’t subclass

Bridging

many parts of Swift don’t bridge

Does this really need to be used in Objective-C?

framework headers can’t be in bridging header

use @import

Partial bridging

-Swift.h will leave out funcs/vars that don’t bridge

Again: does this really need to be bridged?

Type System

properties can have 1 type

protocol Themeable {} class ListViewController: UIViewController, Themeable {}

var themedViewController: // UIViewController, Themeable ????

two workarounds

public protocol ViewControllerProtocol { var view: UIView! { get } var storyboard: UIStoryboard? { get } init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) func viewDidLoad() // etc }

protocol ThemeableViewController: Themeable, ViewControllerProtocol {} var themedViewController: ThemeableViewController

Swift-y but hack-y

var themed: Themeable { get { return self.viewController as! Themeable } set(newThemeable) { if let themedViewController = newThemeable as? UIViewController{ viewController = themedViewController } } }

var viewController: UIViewController init<T where T: Themeable, T: UIViewController>(viewController: T) { self.viewController = viewController }

Also swfit-y also hack-y

Can’t override type with inheritance

🚫Deep object hierarchies

Protocols

Composition instead of inheritance

Protocols and inheritance don’t mix

use POP to mock

Generics

Can’t reference a generic protocol

protocol Holder { typealias Item var items: [Item] { get } }

class Basket<Thing>: Holder{ var items: [Thing] = [] func add(item: Thing) { items.append(item) } }

🚫🚫

var someHolder: Holder var someBasket: Basket

🚫 var someHolder: Holder<Peach> var someBasket: Basket<Peach>

Covariance only works with generic classes

Covariance: If a Cat is an Animal func feed(animal: Animal) can receive a Cat

🚫🚫

typealias Object typealias Object: String typealias RoundObject: Object

generic classes can specify type requirements

class Basket<Thing: Fruit> { var items: [Thing] = [] func add(item: Thing) { items.append(item) } }

🚫

class Basket<Thing: Fruit> { var items: [Thing] = [] func add(item: Thing) { items.append(item) } }

class FruitBasket: Basket<Fruit> {} class PeachBasket: FruitBasket<Peach> {}

🚫class Bag<Stuff> { class Basket<Thing: Stuff> { var items: [Thing] = [] func add(item: Thing) { items.append(item) } } }

Generic non-NSObjects have issues

Explicitly call out class for now

Swift introduces awesome new patterns

Thanks!@MicheleTitolo

Photo Credits

• https://www.flickr.com/photos/83073191@N00/21709516808/

• https://www.flickr.com/photos/64181484@N04/21946459678/

• https://www.flickr.com/photos/66904032@N05/18905223864/

• https://www.flickr.com/photos/27454212@N00/22120629112/

• https://www.flickr.com/photos/8725928@N02/24439195435/

• https://www.flickr.com/photos/28480761@N04/24143685631/