Swift, Generics, Constraints

Online Swift Playground 

//Generics
func add<T: AdditiveArithmetic>(a: T, b: T) -> T {
    return a + b
}
let sum = add(a: 5, b: 5)
print("5 + 5 = \(sum)")

class Point<T>{
    var x:T
    var y:T

    init(x:T, y:T){
        self.x = x
        self.y = y
    }
}

let p1 = Point<Int>(x: 1, y: 2)
let p2: Point<Float> = Point(x: 1.0, y: 2.0)
let p3 = Point(x: 1.0, y: 2.0)
print(p3)

//Constraints
protocol Shape{
    func area() -> Double
}

class Rect: Shape{
    var w: Double
    var h: Double

    init(w:Double, h: Double){
        self.w = w
        self.h = h
    }

    func area() -> Double {
        w * h
    }
}

class Figures<T: Shape>{
    var figures: [T]

    init(figures: [T]){
        self.figures = figures
    }
}

extension Array where Element: Rect {
    func area(){
        forEach { print("area: \($0.area())")}
    }
}

let arr1 = [Rect(w:1, h:1), Rect(w:2, h:2)]
let fig1 = Figures(figures: arr1)
fig1.figures.area()

//associatedtype
protocol Drawable {
    associatedtype Sprite where Sprite: Rect
    func draw(sprite: Sprite)
}

//conditional
protocol Updatable{
    func update()
}

extension Int: Updatable{
    func update(){
        print("update")
    }
}

extension Array: Updatable where Element: Updatable {
    func update(){
        forEach { $0.update()}
    }
}

let arr2 = [1, 2, 3]
1.update()
arr2[0].update()
arr2.update() //x3

//Array
let arr0 = [1, 2, 3] //inference
let arr3: [Int] = [1, 2, 3] //sugar
let arr4 = [Int]() //sugar
let arr5: Array<Int> = [1, 2, 3] //generic
let arr6 = Array<Int>() //generic

//Dictionaries
let dic0 = [1 : "Mike", 2 : "Tom"] //inference
let dic1: [Int : String] = [1 : "Mike", 2 : "Tom"] //sugar
let dic2: [Int : String] = [ : ] //sugar
let dic3: Dictionary<Int, String> = [1 : "Mike", 2 : "Tom"] //generic

//Optionals
enum Optional<T> {
    case some(T)
    case none
}

var op1: Optional<Int> = Optional.some(5)
var op2 = Optional<Int>.some(5)
var op3 = Optional.some(5)
//if op3 == Optional<Int>.none{print("nil")}

var op4: Int? = 5
if op4 == nil {print("nil")}