Swift Introduction

Swift Basic

Back To IOS_Swift

Var

var languageName = "Swift" // is simplified version of      var languageName: String = "Swift"

Constant

let version = 1.0 // let version: Double = 1.0
//:Int, :Bool. :String

let components = "~/Documents/Swift".pathComponents
//["~", "Documents", "Swift"]

Examples

let a = 3, b = 5
let res = "\(a) times \(b) is \(a * b)"
let dog = "dog"
var dog1 = dog + "1"
let a: Character = "a"
let b: Character = "b"
let ab = a + b

Array & Dictionary

//Empty array
var activeInputs: [CIImage] = [] //Must explicitly specify type
//mixed type
var names = ["Anna", "Alex", 42]
var names: String[] = ["Anna", "Alex"]
//Dictionary
var numOfLegs = ["ant": 6, "snake": 0]
//Interate
for x in names {}
for number in 1...5 {}
for num in 0..<5 {} //half close range
for (name, legs) in numOfLegs {} //Tuple
//Modify Array
names += "Sam"
names += ["Hao", "Dan"]
names[0] = "x"
names[3...5] = ["x", "y", "z"]
numOfLegs["spider"] = 273
numOfLegs["spider"] = 8
//Add to array
names.append("ABC")

Initialize Empty Array or Initialize With Content

// Initialize empty array
var array = [String]()
// Initialize empty Dictionary
var dict = Dictionary<String, String>()
// Initialize Array with content and length
var threeDoubles = [Double](count: 3, repeatedValue: 0.0)

Optionals

let possibleLegs: Int? = num
OfLegs["aardvark"] //either get integer or nothing
if possibleLegs == nil {

} else {
  let legCount = possibleLegs! //forcing optional value to it's type
}
//A Simpler way
if let legCount = possibleLegs {

}
Switch legCount {
  case 0: //no break
  case 1: 
  case ExecButton: //match object
  case 1...5:
  case 2,4,6,8:
  default: //required
}
func sayHello(name:String = "default") { //give a default value
  println("Hello \(name)")
}

Optionals in Swift 1.2

// Before Swift 1.2
if let data = widget.dataStream {
  if data.isValid {
    if let source = sourceIP() {
      if let dest = destIP() {
        // do something
      }
    }
  }
}

// After Swift 1.2
if let data = widget.data where data.isValid, let source = sourceIP(), dest = destIP() {
  // do something
}

Tuples

(404, "Not found")
(2, "Banana", 0.42)
let (statusCode, message) = refresh()

Closures

Closure has implicit return!
If you get an error from xcode related to wrong return type, try return something explicitly.

func repeat(count: Int, task: (idx: Int) -> ()) {
    for i in 0..<count {
        task(idx: i)
    }
}
repeat(2, { idx in
    println("hello: " + String(idx))
})

Class

class Vehicle {
  var numOfWheels = 0 //stored properties
  var description: String { //computed properties, has to be var
    get { //get is optional
      return "\(numOfWheels) wheels"
    }
  }
}
let someVehicle = Vehicle() //Auto alloc
//inheritance
class Bicycle: Vehicle {
  init() { //initializer
    super:init()
    numOfWheels = 2
  }
//properties observers
  override var speed: Double {
    willSet {
      if newValue > 65.0 {
        println('warning too fast')
      }
    }
    didSet {
      //oldValue available
    }
  }
  //method
  func accel() {
    speed += 0.1
  }
}

Overriding properties

class Car: Vehicle {
  var speed = 0.0
  init() {
    super.init()
    numOfWheels = 4
  }
  override var description: String {
    return super.description + ", Speed=\(speed) mph"
  }
}

Struct

struct Point {
  var x: Double, y: Double
}
struct Rect {
  var origin: Point
  var size: Size
  //computed property
  var area: Double {
    return size.width * size.height
  }
  //method
  func isBiggerThanRect(other: Rect) => Bool {
    return self.area > other.area
  }
}
//init
var point = Point(x: 0.0, y: 0.0)
var rect = Rect(origin: point, size: size)

Struct and Class

1. struct cannot inherite
2. class is passed by reference. struct is passed by value

Constant and Variables

let window = Window(1.0, 1.0)
//The reference is a constant, cannot change the reference value
can do window.x = 1.0
cannot do window = Window(2.0, 2.0)

var point1 = Point(x: 0.0, y: 0.0) // Point is struct. Since point1 is variable, we can do point1.x = 1.0
let point2 = Point(x: 0.0, y: 0.0) // Cannot do point2.x = 1.0 since point2 is constant

Swift 1.2 conditional assign constant value

let longEdge: CGFloat
 
if isLandscape {
  longEdge = image.calculateWidth()
} else {
  longEdge = image.calculateHeight()
}
 
// you can access longEdge from this point on

Mutating a Structure

struct Point {
  var x,y: Double
  //tell the complier this is a mutating function
  mutating func moveToRightBy(dx: Double) {
    x += dx
  }
}
let point1 = Point(x: 0.0, y: 0.0)
point.moveToRightBy(20.0)
//Error: Cannot mutate constant

Enums

  enum Plannet: Int {
    case Mecury = 1, Venus
    case Earth = 5
  }
  let earth = Planet.Earth.toRaw();
   enum Direction {
    case west, east, north, south
  }
  var direction = Direction.west
  direction = .east
  //example
  label.testAlignment = .Right
  

Enumerations: Associated Values

enum FlightStatus {
  case OnTime
  case Delayed(Int) // minutes
  init() {
    self = OnTime
  }
  var desc: String {
    switch self {
      case OnTime:
        return "on time"
      case Delayed(let minutes):
        return "deplayed by \(minutes) minute(s)"
    }
  }
}
var status = FlightStatus // equals to var status = FlightStatus.OnTime
status = .Delayed(30)
status.desc
//deplayed by 30 minute(s)
//Nested Type
class Flight {
  enum Status {
    case OnTime, Deplayed(Int)
    ...
  }
  var status = Status.OnTime
}

Extensions

extension Size {
  mutating func scaleByFactor(factor: Int) {
    width *= factor
    height *= factor
  }
}
extension Int {
  func repetitions(task: () -> ()) {
    for i in 0..<self {
      task()
    }
  }
}
400.repetitions {
  println("Hello!")
}

Generic Stack Structure (Templates)

struct Stack<T> {
  var elements = <T>[]()
  func push {...}
  func pop {...}
}
var intStack = Stack<int>()
intStack.push(60)
let lastIn = intStack.pop()