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+---
+language: swift
+contributors:
+  - ["Grant Timmerman", "http://github.com/grant"]
+  - ["Christopher Bess", "http://github.com/cbess"]
+  - ["Joey Huang", "http://github.com/kamidox"]
+  - ["Anthony Nguyen", "http://github.com/anthonyn60"]
+filename: learnswift.swift
+---
+
+Swift is a programming language for iOS and OS X development created by Apple. Designed to coexist with Objective-C and to be more resilient against erroneous code, Swift was introduced in 2014 at Apple's developer conference WWDC. It is built with the LLVM compiler included in Xcode 6+.
+
+The official [Swift Programming Language](https://itunes.apple.com/us/book/swift-programming-language/id881256329) book from Apple is now available via iBooks.
+
+See also Apple's [getting started guide](https://developer.apple.com/library/prerelease/ios/referencelibrary/GettingStarted/DevelopiOSAppsSwift/), which has a complete tutorial on Swift.
+
+```swift
+// import a module
+import UIKit
+
+//
+// MARK: Basics
+//
+
+// Xcode supports landmarks to annotate your code and lists them in the jump bar
+// MARK: Section mark
+// TODO: Do something soon
+// FIXME: Fix this code
+
+// In Swift 2, println and print were combined into one print method. Print automatically appends a new line.
+print("Hello, world") // println is now print
+print("Hello, world", appendNewLine: false) // printing without appending a newline
+
+// variables (var) value can change after being set
+// constants (let) value can NOT be changed after being set
+
+var myVariable = 42
+let øπΩ = "value" // unicode variable names
+let π = 3.1415926
+let convenience = "keyword" // contextual variable name
+let weak = "keyword"; let override = "another keyword" // statements can be separated by a semi-colon
+let `class` = "keyword" // backticks allow keywords to be used as variable names
+let explicitDouble: Double = 70
+let intValue = 0007 // 7
+let largeIntValue = 77_000 // 77000
+let label = "some text " + String(myVariable) // Casting
+let piText = "Pi = \(π), Pi 2 = \(π * 2)" // String interpolation
+
+// Build Specific values
+// uses -D build configuration
+#if false
+    print("Not printed")
+    let buildValue = 3
+#else
+    let buildValue = 7
+#endif
+print("Build value: \(buildValue)") // Build value: 7
+
+/*
+    Optionals are a Swift language feature that allows you to store a `Some` or
+    `None` value.
+
+    Because Swift requires every property to have a value, even nil must be
+    explicitly stored as an Optional value.
+
+    Optional<T> is an enum.
+*/
+var someOptionalString: String? = "optional" // Can be nil
+// same as above, but ? is a postfix operator (syntax candy)
+var someOptionalString2: Optional<String> = "optional"
+
+if someOptionalString != nil {
+    // I am not nil
+    if someOptionalString!.hasPrefix("opt") {
+        print("has the prefix")
+    }
+
+    let empty = someOptionalString?.isEmpty
+}
+someOptionalString = nil
+
+// implicitly unwrapped optional
+var unwrappedString: String! = "Value is expected."
+// same as above, but ! is a postfix operator (more syntax candy)
+var unwrappedString2: ImplicitlyUnwrappedOptional<String> = "Value is expected."
+
+if let someOptionalStringConstant = someOptionalString {
+    // has `Some` value, non-nil
+    if !someOptionalStringConstant.hasPrefix("ok") {
+        // does not have the prefix
+    }
+}
+
+// Swift has support for storing a value of any type.
+// AnyObject == id
+// Unlike Objective-C `id`, AnyObject works with any value (Class, Int, struct, etc)
+var anyObjectVar: AnyObject = 7
+anyObjectVar = "Changed value to a string, not good practice, but possible."
+
+/*
+    Comment here
+
+    /*
+        Nested comments are also supported
+    */
+*/
+
+//
+// MARK: Collections
+//
+
+/*
+    Array and Dictionary types are structs. So `let` and `var` also indicate
+    that they are mutable (var) or immutable (let) when declaring these types.
+*/
+
+// Array
+var shoppingList = ["catfish", "water", "lemons"]
+shoppingList[1] = "bottle of water"
+let emptyArray = [String]() // let == immutable
+let emptyArray2 = Array<String>() // same as above
+var emptyMutableArray = [String]() // var == mutable
+
+
+// Dictionary
+var occupations = [
+    "Malcolm": "Captain",
+    "kaylee": "Mechanic"
+]
+occupations["Jayne"] = "Public Relations"
+let emptyDictionary = [String: Float]() // let == immutable
+let emptyDictionary2 = Dictionary<String, Float>() // same as above
+var emptyMutableDictionary = [String: Float]() // var == mutable
+
+
+//
+// MARK: Control Flow
+//
+
+// for loop (array)
+let myArray = [1, 1, 2, 3, 5]
+for value in myArray {
+    if value == 1 {
+        print("One!")
+    } else {
+        print("Not one!")
+    }
+}
+
+// for loop (dictionary)
+var dict = ["one": 1, "two": 2]
+for (key, value) in dict {
+    print("\(key): \(value)")
+}
+
+// for loop (range)
+for i in -1...shoppingList.count {
+    print(i)
+}
+shoppingList[1...2] = ["steak", "peacons"]
+// use ..< to exclude the last number
+
+// while loop
+var i = 1
+while i < 1000 {
+    i *= 2
+}
+
+// do-while loop
+do {
+    print("hello")
+} while 1 == 2
+
+// Switch
+// Very powerful, think `if` statements with syntax candy
+// They support String, object instances, and primitives (Int, Double, etc)
+let vegetable = "red pepper"
+switch vegetable {
+case "celery":
+    let vegetableComment = "Add some raisins and make ants on a log."
+case "cucumber", "watercress":
+    let vegetableComment = "That would make a good tea sandwich."
+case let localScopeValue where localScopeValue.hasSuffix("pepper"):
+    let vegetableComment = "Is it a spicy \(localScopeValue)?"
+default: // required (in order to cover all possible input)
+    let vegetableComment = "Everything tastes good in soup."
+}
+
+
+//
+// MARK: Functions
+//
+
+// Functions are a first-class type, meaning they can be nested
+// in functions and can be passed around
+
+// Function with Swift header docs (format as reStructedText)
+
+/**
+    A greet operation
+
+    - A bullet in docs
+    - Another bullet in the docs
+
+    :param: name A name
+    :param: day A day
+    :returns: A string containing the name and day value.
+*/
+func greet(name: String, day: String) -> String {
+    return "Hello \(name), today is \(day)."
+}
+greet("Bob", "Tuesday")
+
+// similar to above except for the function parameter behaviors
+func greet2(#requiredName: String, externalParamName localParamName: String) -> String {
+    return "Hello \(requiredName), the day is \(localParamName)"
+}
+greet2(requiredName:"John", externalParamName: "Sunday")
+
+// Function that returns multiple items in a tuple
+func getGasPrices() -> (Double, Double, Double) {
+    return (3.59, 3.69, 3.79)
+}
+let pricesTuple = getGasPrices()
+let price = pricesTuple.2 // 3.79
+// Ignore Tuple (or other) values by using _ (underscore)
+let (_, price1, _) = pricesTuple // price1 == 3.69
+print(price1 == pricesTuple.1) // true
+print("Gas price: \(price)")
+
+// Variadic Args
+func setup(numbers: Int...) {
+    // its an array
+    let number = numbers[0]
+    let argCount = numbers.count
+}
+
+// Passing and returning functions
+func makeIncrementer() -> (Int -> Int) {
+    func addOne(number: Int) -> Int {
+        return 1 + number
+    }
+    return addOne
+}
+var increment = makeIncrementer()
+increment(7)
+
+// pass by ref
+func swapTwoInts(inout a: Int, inout b: Int) {
+    let tempA = a
+    a = b
+    b = tempA
+}
+var someIntA = 7
+var someIntB = 3
+swapTwoInts(&someIntA, &someIntB)
+print(someIntB) // 7
+
+
+//
+// MARK: Closures
+//
+var numbers = [1, 2, 6]
+
+// Functions are special case closures ({})
+
+// Closure example.
+// `->` separates the arguments and return type
+// `in` separates the closure header from the closure body
+numbers.map({
+    (number: Int) -> Int in
+    let result = 3 * number
+    return result
+})
+
+// When the type is known, like above, we can do this
+numbers = numbers.map({ number in 3 * number })
+// Or even this
+//numbers = numbers.map({ $0 * 3 })
+
+print(numbers) // [3, 6, 18]
+
+// Trailing closure
+numbers = sorted(numbers) { $0 > $1 }
+
+print(numbers) // [18, 6, 3]
+
+// Super shorthand, since the < operator infers the types
+
+numbers = sorted(numbers, < )
+
+print(numbers) // [3, 6, 18]
+
+//
+// MARK: Structures
+//
+
+// Structures and classes have very similar capabilites
+struct NamesTable {
+    let names = [String]()
+
+    // Custom subscript
+    subscript(index: Int) -> String {
+        return names[index]
+    }
+}
+
+// Structures have an auto-generated (implicit) designated initializer
+let namesTable = NamesTable(names: ["Me", "Them"])
+let name = namesTable[1]
+print("Name is \(name)") // Name is Them
+
+//
+// MARK: Classes
+//
+
+// Classes, structures and its members have three levels of access control
+// They are: internal (default), public, private
+
+public class Shape {
+    public func getArea() -> Int {
+        return 0;
+    }
+}
+
+// All methods and properties of a class are public.
+// If you just need to store data in a
+// structured object, you should use a `struct`
+
+internal class Rect: Shape {
+    var sideLength: Int = 1
+
+    // Custom getter and setter property
+    private var perimeter: Int {
+        get {
+            return 4 * sideLength
+        }
+        set {
+            // `newValue` is an implicit variable available to setters
+            sideLength = newValue / 4
+        }
+    }
+
+    // Lazily load a property
+    // subShape remains nil (uninitialized) until getter called
+    lazy var subShape = Rect(sideLength: 4)
+
+    // If you don't need a custom getter and setter,
+    // but still want to run code before and after getting or setting
+    // a property, you can use `willSet` and `didSet`
+    var identifier: String = "defaultID" {
+        // the `willSet` arg will be the variable name for the new value
+        willSet(someIdentifier) {
+            print(someIdentifier)
+        }
+    }
+
+    init(sideLength: Int) {
+        self.sideLength = sideLength
+        // always super.init last when init custom properties
+        super.init()
+    }
+
+    func shrink() {
+        if sideLength > 0 {
+            --sideLength
+        }
+    }
+
+    override func getArea() -> Int {
+        return sideLength * sideLength
+    }
+}
+
+// A simple class `Square` extends `Rect`
+class Square: Rect {
+    convenience init() {
+        self.init(sideLength: 5)
+    }
+}
+
+var mySquare = Square()
+print(mySquare.getArea()) // 25
+mySquare.shrink()
+print(mySquare.sideLength) // 4
+
+// cast instance
+let aShape = mySquare as Shape
+
+// compare instances, not the same as == which compares objects (equal to)
+if mySquare === mySquare {
+    print("Yep, it's mySquare")
+}
+
+// Optional init
+class Circle: Shape {
+    var radius: Int
+    override func getArea() -> Int {
+        return 3 * radius * radius
+    }
+
+    // Place a question mark postfix after `init` is an optional init
+    // which can return nil
+    init?(radius: Int) {
+        self.radius = radius
+        super.init()
+
+        if radius <= 0 {
+            return nil
+        }
+    }
+}
+
+var myCircle = Circle(radius: 1)
+print(myCircle?.getArea())    // Optional(3)
+print(myCircle!.getArea())    // 3
+var myEmptyCircle = Circle(radius: -1)
+print(myEmptyCircle?.getArea())    // "nil"
+if let circle = myEmptyCircle {
+    // will not execute since myEmptyCircle is nil
+    print("circle is not nil")
+}
+
+
+//
+// MARK: Enums
+//
+
+// Enums can optionally be of a specific type or on their own.
+// They can contain methods like classes.
+
+enum Suit {
+    case Spades, Hearts, Diamonds, Clubs
+    func getIcon() -> String {
+        switch self {
+        case .Spades: return "♤"
+        case .Hearts: return "♡"
+        case .Diamonds: return "♢"
+        case .Clubs: return "♧"
+        }
+    }
+}
+
+// Enum values allow short hand syntax, no need to type the enum type
+// when the variable is explicitly declared
+var suitValue: Suit = .Hearts
+
+// Non-Integer enums require direct raw value assignments
+enum BookName: String {
+    case John = "John"
+    case Luke = "Luke"
+}
+print("Name: \(BookName.John.rawValue)")
+
+// Enum with associated Values
+enum Furniture {
+    // Associate with Int
+    case Desk(height: Int)
+    // Associate with String and Int
+    case Chair(String, Int)
+
+    func description() -> String {
+        switch self {
+        case .Desk(let height):
+            return "Desk with \(height) cm"
+        case .Chair(let brand, let height):
+            return "Chair of \(brand) with \(height) cm"
+        }
+    }
+}
+
+var desk: Furniture = .Desk(height: 80)
+print(desk.description())     // "Desk with 80 cm"
+var chair = Furniture.Chair("Foo", 40)
+print(chair.description())    // "Chair of Foo with 40 cm"
+
+
+//
+// MARK: Protocols
+//
+
+// `protocol`s can require that conforming types have specific
+// instance properties, instance methods, type methods,
+// operators, and subscripts.
+
+protocol ShapeGenerator {
+    var enabled: Bool { get set }
+    func buildShape() -> Shape
+}
+
+// Protocols declared with @objc allow optional functions,
+// which allow you to check for conformance
+@objc protocol TransformShape {
+    optional func reshaped()
+    optional func canReshape() -> Bool
+}
+
+class MyShape: Rect {
+    var delegate: TransformShape?
+
+    func grow() {
+        sideLength += 2
+
+        // Place a question mark after an optional property, method, or
+        // subscript to gracefully ignore a nil value and return nil
+        // instead of throwing a runtime error ("optional chaining").
+        if let allow = self.delegate?.canReshape?() {
+            // test for delegate then for method
+            self.delegate?.reshaped?()
+        }
+    }
+}
+
+
+//
+// MARK: Other
+//
+
+// `extension`s: Add extra functionality to an already existing type
+
+// Square now "conforms" to the `Printable` protocol
+extension Square: Printable {
+    var description: String {
+        return "Area: \(self.getArea()) - ID: \(self.identifier)"
+    }
+}
+
+print("Square: \(mySquare)")
+
+// You can also extend built-in types
+extension Int {
+    var customProperty: String {
+        return "This is \(self)"
+    }
+
+    func multiplyBy(num: Int) -> Int {
+        return num * self
+    }
+}
+
+print(7.customProperty) // "This is 7"
+print(14.multiplyBy(3)) // 42
+
+// Generics: Similar to Java and C#. Use the `where` keyword to specify the
+//   requirements of the generics.
+
+func findIndex<T: Equatable>(array: [T], valueToFind: T) -> Int? {
+    for (index, value) in enumerate(array) {
+        if value == valueToFind {
+            return index
+        }
+    }
+    return nil
+}
+let foundAtIndex = findIndex([1, 2, 3, 4], 3)
+print(foundAtIndex == 2) // true
+
+// Operators:
+// Custom operators can start with the characters:
+//      / = - + * % < > ! & | ^ . ~
+// or
+// Unicode math, symbol, arrow, dingbat, and line/box drawing characters.
+prefix operator !!! {}
+
+// A prefix operator that triples the side length when used
+prefix func !!! (inout shape: Square) -> Square {
+    shape.sideLength *= 3
+    return shape
+}
+
+// current value
+print(mySquare.sideLength) // 4
+
+// change side length using custom !!! operator, increases size by 3
+!!!mySquare
+print(mySquare.sideLength) // 12
+```