標

類，結構和列舉可以定義下標，下標是用於訪問集合，列表或序列的成員元素的快捷方式。

例

struct DaysOfWeek {
  
  var days = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]
  
  subscript(index: Int) -> String {
    get {
      return days[index]
    }
    set {
      days[index] = newValue
    }
  }
}

下標用法

var week = DaysOfWeek()
//you access an element of an array at index by array[index].
debugPrint(week[1])
debugPrint(week[0])
week[0] = "Sunday"
debugPrint(week[0])

下標選項：

下標可以採用任意數量的輸入引數，這些輸入引數可以是任何型別。下標也可以返回任何型別。下標可以使用變數引數和可變引數，但不能使用輸入輸出引數或提供預設引數值。

例：

struct Food {
  
  enum MealTime {
    case Breakfast, Lunch, Dinner
  }
  
  var meals: [MealTime: String] = [:]
  
  subscript (type: MealTime) -> String? {
    get {
      return meals[type]
    }
    set {
      meals[type] = newValue
    }
  }
}

用法

var diet = Food()
diet[.Breakfast] = "Scrambled Eggs"
diet[.Lunch] = "Rice"

debugPrint("I had \(diet[.Breakfast]) for breakfast")