Swift-Defer延迟执行

类似于延迟：

      var sumOfOdd = 0
      for i in 0...10 {
        defer {
          print("Look! It's \(i)---\(sumOfOdd)")
        }
        if i % 2 == 0 {
          continue
        }
        sumOfOdd += i
      }



打印结果：

Look! It's 0---0
Look! It's 1---1
Look! It's 2---1
Look! It's 3---4
Look! It's 4---4
Look! It's 5---9
Look! It's 6---9
Look! It's 7---16
Look! It's 8---16
Look! It's 9---25
Look! It's 10---25

想要某部分代码延迟到作用域结束后执行，defer是个很好的选择