runtime

http://yulingtianxia.com/blog/2014/11/05/objective-c-runtime/

http://blog.sunnyxx.com/2016/08/13/reunderstanding-runtime-0/

http://www.cnblogs.com/jys509/p/5207159.html

http://blog.csdn.net/indulgein/article/details/51111472

http://www.jianshu.com/p/25a319aee33d

http://www.jianshu.com/p/364eab29f4f5

http://blog.csdn.net/chenyufeng1991/article/details/51931320