Swift学习笔记扩展

extension Double {
    var km: Double { return self * 1_000.0 }
    var m: Double { return self }
    var cm: Double { return self / 100.0 }
    var mm: Double { return self / 1_000.0 }
    var ft: Double { return self / 3.28084 }
}
extension Int {
    var mm: Int { return self * 10000 }
}

let oneInch = 25.mm
let threeFeet = 3.ft
let aMarathon = 42.km + 195.m

let a = 1.mm

struct Size {
    var width = 0.0, height = 0.0
}
struct Point {
    var x = 0.0, y = 0.0
}
struct Rect {
    var origin = Point()
    var size = Size()
}

let defaultRect = Rect()
let memberwiseRect = Rect(origin: Point(x: 2.0, y: 2.0),
    size: Size(width: 5.0, height: 5.0))

extension Rect {
    init(center: Point, size: Size) {
        let originX = center.x - (size.width / 2)
        let originY = center.y - (size.height / 2)
        self.init(origin: Point(x: originX, y: originY), size: size)
    }
}

let centerRect = Rect(center: Point(x: 4.0, y: 4.0),
    size: Size(width: 3.0, height: 3.0))

extension Int {
    func repetitions(task: () -> ()) {
        for _ in 0..<self {
            task()
        }
    }
}
3.repetitions({
    println("Hello!")
})
3.repetitions{
    println("Goodbye!")
}
extension Int {

    mutating func square() {
        self = self * self
    }
}

var someInt = 3
someInt.square()

extension Int {
    subscript(var digitIndex: Int) -> Int {
        var decimalBase = 1
        while digitIndex > 0 {
            decimalBase *= 10
            --digitIndex
        }
        return (self / decimalBase) % 10
    }
}

746381295[0]
746381295[1]

extension Int {
    enum Kind {
        case Negative, Zero, Positive
    }
    var kind: Kind {
        switch self {
        case 0:
            return .Zero
        case let x where x>0:
            return .Positive
        default:
            return .Negative
        }
    }
}

func printIntegerKinds(numbers: [Int]){
    for number in numbers {
        switch number.kind {
        case .Negative:
            print("- ")
        case .Zero:
            print("0 ")
        case .Positive:
            print("+ ")
        }
    }
    println()
}
printIntegerKinds([3, 19, -27, 0, -6, 0, 7])

swift 里的扩展，比C#里的扩展方法更加强大

可以扩展方法，扩展构造器，扩展嵌套类型，扩展属性等。