1. 
bt -- 显示当前线程调用堆栈
2. 
e -- 执行表达式，动态修改当前线程变量的值
3. 
frame variable -- 打印当前堆栈所有变量值
4. 
expr -O --language objC -- 0x000000000 -- 打印当前内存地址内容
5. 
-- 打印视图层级结构
swift 3.0: po let sub = view.perform("recursiveDescription"); print(sub)
swift 2.0: po view.performSelector("recursiveDescription")
objective-c: [self.view recursiveDescription]
(转自： http://stackoverflow.com/questions/25900606/recursivedescription-method-in-swift)