Design Patterns implemented in Swift 2.2

A short cheat-sheet with Xcode 7.3 Playground (Design-Patterns.playground.zip).

👷 Project maintained by: @nsmeme (Oktawian Chojnacki)

⚠️ See my newest project: OOD-Principles-In-Swift

Table of Contents

Behavioral
Creational
Structural

Behavioral

import Swift
import Foundation

🐝 Chain Of Responsibility

The chain of responsibility pattern is used to process varied requests, each of which may be dealt with by a different handler.

Example:

class MoneyPile {
    let value: Int
    var quantity: Int
    var nextPile: MoneyPile?
    
    init(value: Int, quantity: Int, nextPile: MoneyPile?) {
        self.value = value
        self.quantity = quantity
        self.nextPile = nextPile
    }
    
    func canWithdraw(v: Int) -> Bool {

        var v = v

        func canTakeSomeBill(want: Int) -> Bool {
            return (want / self.value) > 0
        }
        
        var q = self.quantity

        while canTakeSomeBill(v) {

            if q == 0 {
                break
            }

            v -= self.value
            q -= 1
        }

        if v == 0 {
            return true
        } else if let next = self.nextPile {
            return next.canWithdraw(v)
        }

        return false
    }
}

class ATM {
    private var hundred: MoneyPile
    private var fifty: MoneyPile
    private var twenty: MoneyPile
    private var ten: MoneyPile
    
    private var startPile: MoneyPile {
        return self.hundred
    }
    
    init(hundred: MoneyPile, 
           fifty: MoneyPile, 
          twenty: MoneyPile, 
             ten: MoneyPile) {

        self.hundred = hundred
        self.fifty = fifty
        self.twenty = twenty
        self.ten = ten
    }
    
    func canWithdraw(value: Int) -> String {
        return "Can withdraw: \(self.startPile.canWithdraw(value))"
    }
}

Usage

// Create piles of money and link them together 10 < 20 < 50 < 100.**
let ten = MoneyPile(value: 10, quantity: 6, nextPile: nil)
let twenty = MoneyPile(value: 20, quantity: 2, nextPile: ten)
let fifty = MoneyPile(value: 50, quantity: 2, nextPile: twenty)
let hundred = MoneyPile(value: 100, quantity: 1, nextPile: fifty)

// Build ATM.
var atm = ATM(hundred: hundred, fifty: fifty, twenty: twenty, ten: ten)
atm.canWithdraw(310) // Cannot because ATM has only 300
atm.canWithdraw(100) // Can withdraw - 1x100
atm.canWithdraw(165) // Cannot withdraw because ATM doesn't has bill with value of 5
atm.canWithdraw(30)  // Can withdraw - 1x20, 2x10

👫 Command

The command pattern is used to express a request, including the call to be made and all of its required parameters, in a command object. The command may then be executed immediately or held for later use.

Example:

protocol DoorCommand {
    func execute() -> String
}

class OpenCommand : DoorCommand {
    let doors:String

    required init(doors: String) {
        self.doors = doors
    }
    
    func execute() -> String {
        return "Opened \(doors)"
    }
}

class CloseCommand : DoorCommand {
    let doors:String

    required init(doors: String) {
        self.doors = doors
    }
    
    func execute() -> String {
        return "Closed \(doors)"
    }
}

class HAL9000DoorsOperations {
    let openCommand: DoorCommand
    let closeCommand: DoorCommand
    
    init(doors: String) {
        self.openCommand = OpenCommand(doors:doors)
        self.closeCommand = CloseCommand(doors:doors)
    }
    
    func close() -> String {
        return closeCommand.execute()
    }
    
    func open() -> String {
        return openCommand.execute()
    }
}

Usage:

let podBayDoors = "Pod Bay Doors"
let doorModule = HAL9000DoorsOperations(doors:podBayDoors)

doorModule.open()
doorModule.close()

🎶 Interpreter

The interpreter pattern is used to evaluate sentences in a language.

Example

protocol IntegerExp {
    func evaluate(context: IntegerContext) -> Int
    func replace(character: Character, integerExp: IntegerExp) -> IntegerExp
    func copy() -> IntegerExp
}

class IntegerContext {
    private var data: [Character:Int] = [:]
    
    func lookup(name: Character) -> Int {
        return self.data[name]!
    }
    
    func assign(integerVarExp: IntegerVarExp, value: Int) {
        self.data[integerVarExp.name] = value
    }
}

class IntegerVarExp: IntegerExp {
    let name: Character
    
    init(name: Character) {
        self.name = name
    }
    
    func evaluate(context: IntegerContext) -> Int {
        return context.lookup(self.name)
    }
    
    func replace(name: Character, integerExp: IntegerExp) -> IntegerExp {
        if name == self.name {
            return integerExp.copy()
        } else {
            return IntegerVarExp(name: self.name)
        }
    }
    
    func copy() -> IntegerExp {
        return IntegerVarExp(name: self.name)
    }
}

class AddExp: IntegerExp {
    private var operand1: IntegerExp
    private var operand2: IntegerExp
    
    init(op1: IntegerExp, op2: IntegerExp) {
        self.operand1 = op1
        self.operand2 = op2
    }
    
    func evaluate(context: IntegerContext) -> Int {
        return self.operand1.evaluate(context) + self.operand2.evaluate(context)
    }
    
    func replace(character: Character, integerExp: IntegerExp) -> IntegerExp {
        return AddExp(op1: operand1.replace(character, integerExp: integerExp),
            op2: operand2.replace(character, integerExp: integerExp))
    }
    
    func copy() -> IntegerExp {
        return AddExp(op1: self.operand1, op2: self.operand2)
    }
}

Usage

var expression: IntegerExp?
var intContext = IntegerContext()

var a = IntegerVarExp(name: "A")
var b = IntegerVarExp(name: "B")
var c = IntegerVarExp(name: "C")

expression = AddExp(op1: a, op2: AddExp(op1: b, op2: c)) // a + (b + c)

intContext.assign(a, value: 2)
intContext.assign(b, value: 1)
intContext.assign(c, value: 3)

var result = expression?.evaluate(intContext)

🍫 Iterator

The iterator pattern is used to provide a standard interface for traversing a collection of items in an aggregate object without the need to understand its underlying structure.

Example:

struct NovellasCollection<T> {
    let novellas: [T]
}

extension NovellasCollection: SequenceType {
    typealias Generator = AnyGenerator<T>
    
    func generate() -> AnyGenerator<T> {
        var i = 0
        return AnyGenerator { i += 1; return i >= self.novellas.count ? nil : self.novellas[i] }
    }
}

Usage

let greatNovellas = NovellasCollection(novellas:["Mist"])

for novella in greatNovellas {
    print("I've read: \(novella)")
}

💐 Mediator

The mediator pattern is used to reduce coupling between classes that communicate with each other. Instead of classes communicating directly, and thus requiring knowledge of their implementation, the classes send messages via a mediator object.

Example

class Colleague {
    let name: String
    let mediator: Mediator
    
    init(name: String, mediator: Mediator) {
        self.name = name
        self.mediator = mediator
    }
    
    func send(message: String) {
        mediator.send(message, colleague: self)
    }
    
    func receive(message: String) {
        assert(false, "Method should be overriden")
    }
}

protocol Mediator {
    func send(message: String, colleague: Colleague)
}

class MessageMediator: Mediator {
    private var colleagues: [Colleague] = []
    
    func addColleague(colleague: Colleague) {
        colleagues.append(colleague)
    }
    
    func send(message: String, colleague: Colleague) {
        for c in colleagues {
            if c !== colleague { //for simplicity we compare object references
                c.receive(message)
            }
        }
    }
}

class ConcreteColleague: Colleague {
    override func receive(message: String) {
        print("Colleague \(name) received: \(message)")
    }
}

Usage

let messagesMediator = MessageMediator()
let user0 = ConcreteColleague(name: "0", mediator: messagesMediator)
let user1 = ConcreteColleague(name: "1", mediator: messagesMediator)
messagesMediator.addColleague(user0)
messagesMediator.addColleague(user1)

user0.send("Hello") // user1 receives message

💾 Memento

The memento pattern is used to capture the current state of an object and store it in such a manner that it can be restored at a later time without breaking the rules of encapsulation.

Example

typealias Memento = Dictionary<NSObject, AnyObject>

let DPMementoKeyChapter = "com.valve.halflife.chapter"
let DPMementoKeyWeapon = "com.valve.halflife.weapon"
let DPMementoGameState = "com.valve.halflife.state"

Originator

class GameState {
    var chapter: String = ""
    var weapon: String = ""

    func toMemento() -> Memento {
        return [ DPMementoKeyChapter:chapter, DPMementoKeyWeapon:weapon ]
    }

    func restoreFromMemento(memento: Memento) {
        chapter = memento[DPMementoKeyChapter] as? String ?? "n/a"
        weapon = memento[DPMementoKeyWeapon] as? String ?? "n/a"
    }
}

Caretaker

enum CheckPoint {
    static func saveState(memento: Memento, keyName: String = DPMementoGameState) {
        let defaults = NSUserDefaults.standardUserDefaults()
        defaults.setObject(memento, forKey: keyName)
        defaults.synchronize()
    }

    static func restorePreviousState(keyName keyName: String = DPMementoGameState) -> Memento {
        let defaults = NSUserDefaults.standardUserDefaults()

        return defaults.objectForKey(keyName) as? Memento ?? Memento()
    }
}

Usage

var gameState = GameState()
gameState.restoreFromMemento(CheckPoint.restorePreviousState())

gameState.chapter = "Black Mesa Inbound"
gameState.weapon = "Crowbar"
CheckPoint.saveState(gameState.toMemento())

gameState.chapter = "Anomalous Materials"
gameState.weapon = "Glock 17"
gameState.restoreFromMemento(CheckPoint.restorePreviousState())

gameState.chapter = "Unforeseen Consequences"
gameState.weapon = "MP5"
CheckPoint.saveState(gameState.toMemento(), keyName: "gameState2")

gameState.chapter = "Office Complex"
gameState.weapon = "Crossbow"
CheckPoint.saveState(gameState.toMemento())

gameState.restoreFromMemento(CheckPoint.restorePreviousState(keyName: "gameState2"))

👓 Observer

The observer pattern is used to allow an object to publish changes to its state. Other objects subscribe to be immediately notified of any changes.

Example

protocol PropertyObserver : class {
    func willChangePropertyName(propertyName:String, newPropertyValue:AnyObject?)
    func didChangePropertyName(propertyName:String, oldPropertyValue:AnyObject?)
}

class TestChambers {

    weak var observer:PropertyObserver?

    var testChamberNumber: Int = 0 {
        willSet(newValue) {
            observer?.willChangePropertyName("testChamberNumber", newPropertyValue:newValue)
        }
        didSet {
            observer?.didChangePropertyName("testChamberNumber", oldPropertyValue:oldValue)
        }
    }
}

class Observer : PropertyObserver {
    func willChangePropertyName(propertyName: String, newPropertyValue: AnyObject?) {
        if newPropertyValue as? Int == 1 {
            print("Okay. Look. We both said a lot of things that you're going to regret.")
        }
    }

    func didChangePropertyName(propertyName: String, oldPropertyValue: AnyObject?) {
        if oldPropertyValue as? Int == 0 {
            print("Sorry about the mess. I've really let the place go since you killed me.")
        }
    }
}

Usage

var observerInstance = Observer()
var testChambers = TestChambers()
testChambers.observer = observerInstance
testChambers.testChamberNumber++

🐉 State

The state pattern is used to alter the behaviour of an object as its internal state changes. The pattern allows the class for an object to apparently change at run-time.

Example

class Context {
	private var state: State = UnauthorizedState()

    var isAuthorized: Bool {
        get { return state.isAuthorized(self) }
    }

    var userId: String? {
        get { return state.userId(self) }
    }

	func changeStateToAuthorized(userId userId: String) {
		state = AuthorizedState(userId: userId)
	}

	func changeStateToUnauthorized() {
		state = UnauthorizedState()
	}
    
}

protocol State {
	func isAuthorized(context: Context) -> Bool
	func userId(context: Context) -> String?
}

class UnauthorizedState: State {
	func isAuthorized(context: Context) -> Bool { return false }

	func userId(context: Context) -> String? { return nil }
}

class AuthorizedState: State {
	let userId: String

	init(userId: String) { self.userId = userId }

	func isAuthorized(context: Context) -> Bool { return true }

	func userId(context: Context) -> String? { return userId }
}

Usage

let context = Context()
(context.isAuthorized, context.userId)
context.changeStateToAuthorized(userId: "admin")
(context.isAuthorized, context.userId) // now logged in as "admin"
context.changeStateToUnauthorized()
(context.isAuthorized, context.userId)

💡 Strategy

The strategy pattern is used to create an interchangeable family of algorithms from which the required process is chosen at run-time.

Example

protocol PrintStrategy {
    func printString(string: String) -> String
}

class Printer {

    let strategy: PrintStrategy
    
    func printString(string: String) -> String {
        return self.strategy.printString(string)
    }
    
    init(strategy: PrintStrategy) {
        self.strategy = strategy
    }
}

class UpperCaseStrategy : PrintStrategy {
    func printString(string:String) -> String {
        return string.uppercaseString
    }
}

class LowerCaseStrategy : PrintStrategy {
    func printString(string:String) -> String {
        return string.lowercaseString
    }
}

Usage

var lower = Printer(strategy:LowerCaseStrategy())
lower.printString("O tempora, o mores!")

var upper = Printer(strategy:UpperCaseStrategy())
upper.printString("O tempora, o mores!")

🏃 Visitor

The visitor pattern is used to separate a relatively complex set of structured data classes from the functionality that may be performed upon the data that they hold.

Example

protocol PlanetVisitor {
	func visit(planet: PlanetAlderaan)
	func visit(planet: PlanetCoruscant)
	func visit(planet: PlanetTatooine)
}

protocol Planet {
	func accept(visitor: PlanetVisitor)
}

class PlanetAlderaan: Planet {
	func accept(visitor: PlanetVisitor) { visitor.visit(self) }
}
class PlanetCoruscant: Planet {
	func accept(visitor: PlanetVisitor) { visitor.visit(self) }
}
class PlanetTatooine: Planet {
	func accept(visitor: PlanetVisitor) { visitor.visit(self) }
}

class NameVisitor: PlanetVisitor {
	var name = ""

	func visit(planet: PlanetAlderaan)  { name = "Alderaan" }
	func visit(planet: PlanetCoruscant) { name = "Coruscant" }
	func visit(planet: PlanetTatooine)  { name = "Tatooine" }
}

Usage

let planets: [Planet] = [PlanetAlderaan(), PlanetCoruscant(), PlanetTatooine()]

let names = planets.map { (planet: Planet) -> String in
	let visitor = NameVisitor()
	planet.accept(visitor)
	return visitor.name
}

names

Creational

import Swift
import Foundation

🌰 Abstract Factory

The abstract factory pattern is used to provide a client with a set of related or dependant objects. The "family" of objects created by the factory are determined at run-time.

Example

Protocols

protocol Decimal {
    func stringValue() -> String
    // factory
    static func make(string : String) -> Decimal
}

typealias NumberFactory = (String) -> Decimal

// Number implementations with factory methods

struct NextStepNumber : Decimal {
    private var nextStepNumber : NSNumber

    func stringValue() -> String { return nextStepNumber.stringValue }
    
    // factory
    static func make(string : String) -> Decimal {
        return NextStepNumber(nextStepNumber:NSNumber(longLong:(string as NSString).longLongValue))
    }
}

struct SwiftNumber : Decimal {
    private var swiftInt : Int

    func stringValue() -> String { return "\(swiftInt)" }
    
    // factory
    static func make(string : String) -> Decimal {
        return SwiftNumber(swiftInt:(string as NSString).integerValue)
    }
}

Abstract factory

enum NumberType {
    case NextStep, Swift
}

enum NumberHelper {
    static func factoryFor(type : NumberType) -> NumberFactory {
        switch type {
        case .NextStep:
            return NextStepNumber.make
        case .Swift:
            return SwiftNumber.make
        }
    }
}

Usage

let factoryOne = NumberHelper.factoryFor(.NextStep)
let numberOne = factoryOne("1")
numberOne.stringValue()

let factoryTwo = NumberHelper.factoryFor(.Swift)
let numberTwo = factoryTwo("2")
numberTwo.stringValue()

👷 Builder

The builder pattern is used to create complex objects with constituent parts that must be created in the same order or using a specific algorithm. An external class controls the construction algorithm.

Example

class DeathStarBuilder {

    var x: Double?
    var y: Double?
    var z: Double?

    typealias BuilderClosure = (DeathStarBuilder) -> ()

    init(buildClosure: BuilderClosure) {
        buildClosure(self)
    }
}

struct DeathStar : CustomStringConvertible {

    let x: Double
    let y: Double
    let z: Double

    init?(builder: DeathStarBuilder) {

        if let x = builder.x, y = builder.y, z = builder.z {
            self.x = x
            self.y = y
            self.z = z
        } else {
            return nil
        }
    }

    var description:String {
        return "Death Star at (x:\(x) y:\(y) z:\(z))"
    }
}

Usage

let empire = DeathStarBuilder { builder in
    builder.x = 0.1
    builder.y = 0.2
    builder.z = 0.3
}

let deathStar = DeathStar(builder:empire)

🏭 Factory Method

The factory pattern is used to replace class constructors, abstracting the process of object generation so that the type of the object instantiated can be determined at run-time.

Example

protocol Currency {
    func symbol() -> String
    func code() -> String
}

class Euro : Currency {
    func symbol() -> String {
        return "€"
    }
    
    func code() -> String {
        return "EUR"
    }
}

class UnitedStatesDolar : Currency {
    func symbol() -> String {
        return "$"
    }
    
    func code() -> String {
        return "USD"
    }
}

enum Country {
    case UnitedStates, Spain, UK, Greece
}

enum CurrencyFactory {
    static func currencyForCountry(country:Country) -> Currency? {

        switch country {
            case .Spain, .Greece :
                return Euro()
            case .UnitedStates :
                return UnitedStatesDolar()
            default:
                return nil
        }
        
    }
}

Usage

let noCurrencyCode = "No Currency Code Available"

CurrencyFactory.currencyForCountry(.Greece)?.code() ?? noCurrencyCode
CurrencyFactory.currencyForCountry(.Spain)?.code() ?? noCurrencyCode
CurrencyFactory.currencyForCountry(.UnitedStates)?.code() ?? noCurrencyCode
CurrencyFactory.currencyForCountry(.UK)?.code() ?? noCurrencyCode

🃏 Prototype

The prototype pattern is used to instantiate a new object by copying all of the properties of an existing object, creating an independent clone. This practise is particularly useful when the construction of a new object is inefficient.

Example

class ChungasRevengeDisplay {
    var name: String?
    let font: String

    init(font: String) {
        self.font = font
    }

    func clone() -> ChungasRevengeDisplay {
        return ChungasRevengeDisplay(font:self.font)
    }
}

Usage

let Prototype = ChungasRevengeDisplay(font:"GotanProject")

let Philippe = Prototype.clone()
Philippe.name = "Philippe"

let Christoph = Prototype.clone()
Christoph.name = "Christoph"

let Eduardo = Prototype.clone()
Eduardo.name = "Eduardo"

💍 Singleton

The singleton pattern ensures that only one object of a particular class is ever created. All further references to objects of the singleton class refer to the same underlying instance. There are very few applications, do not overuse this pattern!

Example:

class DeathStarSuperlaser {
    static let sharedInstance = DeathStarSuperlaser()

    private init() {
        // Private initialization to ensure just one instance is created.
    }
}

Usage:

let laser = DeathStarSuperlaser.sharedInstance

Structural

import Swift
import Foundation

🔌 Adapter

The adapter pattern is used to provide a link between two otherwise incompatible types by wrapping the "adaptee" with a class that supports the interface required by the client.

Example

protocol OlderDeathStarSuperLaserAiming {
    var angleV: NSNumber {get}
    var angleH: NSNumber {get}
}

Adaptee

struct DeathStarSuperlaserTarget {
    let angleHorizontal: Double
    let angleVertical: Double

    init(angleHorizontal:Double, angleVertical:Double) {
        self.angleHorizontal = angleHorizontal
        self.angleVertical = angleVertical
    }
}

Adapter

struct OldDeathStarSuperlaserTarget : OlderDeathStarSuperLaserAiming {
    private let target : DeathStarSuperlaserTarget

    var angleV:NSNumber {
        return NSNumber(double: target.angleVertical)
    }

    var angleH:NSNumber {
        return NSNumber(double: target.angleHorizontal)
    }

    init(_ target:DeathStarSuperlaserTarget) {
        self.target = target
    }
}

Usage

let target = DeathStarSuperlaserTarget(angleHorizontal: 14.0, angleVertical: 12.0)
let oldFormat = OldDeathStarSuperlaserTarget(target)

oldFormat.angleH
oldFormat.angleV

🌉 Bridge

The bridge pattern is used to separate the abstract elements of a class from the implementation details, providing the means to replace the implementation details without modifying the abstraction.

Example

protocol Switch {
    var appliance: Appliance {get set}
    func turnOn()
}

protocol Appliance {
    func run()
}

class RemoteControl: Switch {
    var appliance: Appliance

    func turnOn() {
        self.appliance.run()
    }
    
    init(appliance: Appliance) {
        self.appliance = appliance
    }
}

class TV: Appliance {
    func run() {
        print("tv turned on");
    }
}

class VacuumCleaner: Appliance {
    func run() {
        print("vacuum cleaner turned on")
    }
}

Usage

var tvRemoteControl = RemoteControl(appliance: TV())
tvRemoteControl.turnOn()

var fancyVacuumCleanerRemoteControl = RemoteControl(appliance: VacuumCleaner())
fancyVacuumCleanerRemoteControl.turnOn()

🌿 Composite

The composite pattern is used to create hierarchical, recursive tree structures of related objects where any element of the structure may be accessed and utilised in a standard manner.

Example

Component

protocol Shape {
    func draw(fillColor: String)
}

Leafs

 
class Square : Shape {
    func draw(fillColor: String) {
        print("Drawing a Square with color \(fillColor)")
    }
}

class Circle : Shape {
    func draw(fillColor: String) {
        print("Drawing a circle with color \(fillColor)")
    }
}

Composite

class Whiteboard : Shape {
    lazy var shapes = [Shape]()
    
    init(_ shapes:Shape...) {
        self.shapes = shapes
    }
    
    func draw(fillColor:String) {
        for shape in self.shapes {
            shape.draw(fillColor)
        }
    }
}

Usage:

var whiteboard = Whiteboard(Circle(), Square())
whiteboard.draw("Red")

🍧 Decorator

The decorator pattern is used to extend or alter the functionality of objects at run- time by wrapping them in an object of a decorator class. This provides a flexible alternative to using inheritance to modify behaviour.

Example

protocol Coffee {
    func getCost() -> Double
    func getIngredients() -> String
}

class SimpleCoffee: Coffee {
    func getCost() -> Double {
        return 1.0
    }

    func getIngredients() -> String {
        return "Coffee"
    }
}

class CoffeeDecorator: Coffee {
    private let decoratedCoffee: Coffee
    private let ingredientSeparator: String = ", "

    required init(decoratedCoffee: Coffee) {
        self.decoratedCoffee = decoratedCoffee
    }

    func getCost() -> Double {
        return decoratedCoffee.getCost()
    }

    func getIngredients() -> String {
        return decoratedCoffee.getIngredients()
    }
}

class Milk: CoffeeDecorator {
    required init(decoratedCoffee: Coffee) {
        super.init(decoratedCoffee: decoratedCoffee)
    }

    override func getCost() -> Double {
        return super.getCost() + 0.5
    }

    override func getIngredients() -> String {
        return super.getIngredients() + ingredientSeparator + "Milk"
    }
}

class WhipCoffee: CoffeeDecorator {
    required init(decoratedCoffee: Coffee) {
        super.init(decoratedCoffee: decoratedCoffee)
    }

    override func getCost() -> Double {
        return super.getCost() + 0.7
    }

    override func getIngredients() -> String {
        return super.getIngredients() + ingredientSeparator + "Whip"
    }
}

Usage:

var someCoffee: Coffee = SimpleCoffee()
print("Cost : \(someCoffee.getCost()); Ingredients: \(someCoffee.getIngredients())")
someCoffee = Milk(decoratedCoffee: someCoffee)
print("Cost : \(someCoffee.getCost()); Ingredients: \(someCoffee.getIngredients())")
someCoffee = WhipCoffee(decoratedCoffee: someCoffee)
print("Cost : \(someCoffee.getCost()); Ingredients: \(someCoffee.getIngredients())")

🎁 Façade

The facade pattern is used to define a simplified interface to a more complex subsystem.

Example

enum Eternal {

    static func setObject(value: AnyObject!, forKey defaultName: String!) {
        let defaults:NSUserDefaults = NSUserDefaults.standardUserDefaults()
        defaults.setObject(value, forKey:defaultName)
        defaults.synchronize()
    }

    static func objectForKey(defaultName: String!) -> AnyObject! {
        let defaults:NSUserDefaults = NSUserDefaults.standardUserDefaults()

        return defaults.objectForKey(defaultName)
    }

}

Usage

Eternal.setObject("Disconnect me. I’d rather be nothing", forKey:"Bishop")
Eternal.objectForKey("Bishop")

☔ Protection Proxy

The proxy pattern is used to provide a surrogate or placeholder object, which references an underlying object. Protection proxy is restricting access.

Example

protocol DoorOperator {
    func openDoors(doors: String) -> String
}

class HAL9000 : DoorOperator {
    func openDoors(doors: String) -> String {
        return ("HAL9000: Affirmative, Dave. I read you. Opened \(doors).")
    }
}

class CurrentComputer : DoorOperator {
    private var computer: HAL9000!

    func authenticateWithPassword(pass: String) -> Bool {

        guard pass == "pass" else {
            return false;
        }

        computer = HAL9000()

        return true
    }

    func openDoors(doors: String) -> String {

        guard computer != nil else {
            return "Access Denied. I'm afraid I can't do that."
        }

        return computer.openDoors(doors)
    }
}

Usage

let computer = CurrentComputer()
let doors = "Pod Bay Doors"

computer.openDoors(doors)

computer.authenticateWithPassword("pass")
computer.openDoors(doors)

🍬 Virtual Proxy

The proxy pattern is used to provide a surrogate or placeholder object, which references an underlying object. Virtual proxy is used for loading object on demand.

Example

protocol HEVSuitMedicalAid {
    func administerMorphine() -> String
}

class HEVSuit : HEVSuitMedicalAid {
    func administerMorphine() -> String {
        return "Morphine aministered."
    }
}

class HEVSuitHumanInterface : HEVSuitMedicalAid {
    lazy private var physicalSuit: HEVSuit = HEVSuit()

    func administerMorphine() -> String {
        return physicalSuit.administerMorphine()
    }
}

Usage

let humanInterface = HEVSuitHumanInterface()
humanInterface.administerMorphine()

Info

📖 Descriptions from: Gang of Four Design Patterns Reference Sheet

🚀 How to generate playground (+zip) from source: GENERATE.md

License

ChristopherBell/Design-Patterns-In-Swift

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