http://winsystem.ctocio.com.cn/304/12129804.shtml
http://stackoverflow.com/questions/2657810/deep-copy-vs-shallow-copy
http://www.php.net/manual/en/language.oop5.cloning.php
搜 deep copy
http://winsystem.ctocio.com.cn/304/12129804.shtml
http://stackoverflow.com/questions/2657810/deep-copy-vs-shallow-copy
http://www.php.net/manual/en/language.oop5.cloning.php
搜 deep copy