深入解析Swift语言编程中的可选链

   var area = [radius]()
   var cprint: Int {
      return area.count
   }
   
   subscript(i: Int) -> radius {
      get {
         return area[i]
      }
      set {
         area[i] = newValue
      }
   }
   func circleprint() {
      println("The number of rooms is (cprint)")
   }
   var rectarea: circumference?
}

class radius {
   let radiusname: String
   init(radiusname: String) { self.radiusname = radiusname }
}

class circumference {
   var circumName: String?
   var circumNumber: String?
   var circumarea: String?
   
   func buildingIdentifier() -> String? {
      if circumName != nil {
         return circumName
      } else if circumNumber != nil {
         return circumNumber
      } else {
         return nil
      }
   }
}

let circname = rectangle()
circname.print?[0] = radius(radiusname: "Diameter")

let printing = circle()
printing.area.append(radius(radiusname: "Units"))
printing.area.append(radius(radiusname: "Meter"))
circname.print = printing

if let radiusName = circname.print?[0].radiusname {
   println("Radius is measured in (radiusName).")
} else {
   println("Radius is not specified.")
}

当我们使用 playground 运行上面的程序，得到以下结果。

 

Area of circle is not specified

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