ios面试题

1,category和extension的区别

2，retain和copy还有assign的区别  https://blog.csdn.net/u012165769/article/details/50776298

3，iOS block和delegate的区别  https://www.jianshu.com/p/6bba9b4a25d5  https://www.jianshu.com/p/308e3cf7c985