พร็อพเพอร์ตีและซับสคริปต์

struct DataLoader {
    lazy var data: [Int] = {
        print("Loading...")
        return [1,2,3]
    }()
}
var loader = DataLoader()
print("before access")
print(loader.data)

struct Circle {
    var radius: Double
    var diameter: Double {
        get { return radius * 2 }
        set { radius = newValue / 2 }
    }
}
var c = Circle(radius: 5)
print(c.diameter)  // 10
c.diameter = 20
print(c.radius)    // 10

class Account {
    var balance: Double = 0 {
        willSet { print("Will set to", newValue) }
        didSet  { print("Did set from", oldValue) }
    }
}
var a = Account()
a.balance = 50

struct TimesTable {
    let multiplier: Int
    subscript(i: Int) -> Int {
        return multiplier * i
    }
}
let three = TimesTable(multiplier: 3)
print(three[4])   // 12

struct Matrix {
    var grid: [[Int]]
    subscript(row: Int, col: Int) -> Int {
        return grid[row][col]
    }
}
let m = Matrix(grid:[[1,2],[3,4]])
print(m[1,0])   // 3