swift 2.0 defer关键词

defer {
 　　 //do something      
}

func lookforSomething(name:String) throws{  
  //这里是作用域1 整个函数作用域

  print("1-1")
  if name == ""{
    //这里是作用域2 if的作用域
    print("2-1")
    defer{
      print("2-2")
    }
    print("2-3")
  }
  print("1-2")
  defer{
    print("1-3")
  }
  print("1-4")

  if name == "hello"{
    //作用域3
    print("3-1")
    defer{
      print("3-2")
    }
    print("3-3")
    defer{
      print("3-4")
    }
  }
}

try! lookforSomething("")
输出结果为：

    1-1

    2-1

    2-3

    2-2

    1-2

    1-4

    1-3

try! lookforSomething("hello")
输出结果为：

    1-1

    1-2

    1-4

    3-1

    3-3

    3-4

    3-2

    1-3

public class MyNewType : NSObject {
public var myOptionalField:Float? {
        willSet {
            if let newValue = newValue {
                print("I‘m going to change to \(newValue)")
            }
        }
        didSet {
            if let myOptionalField = self.myOptionalField {
                print("Now I‘m \(myOptionalField)")
            }
        }
    }

    override public init() {
        super.init()

        // Non-defered
        self.myOptionalField = 6.28

        // Defered
        defer {
            self.myOptionalField = 3.14
        }
    }
}

I‘m going to change to 3.14
Now I‘m 3.14