ruby 的动态特性

http://hi.baidu.com/firerails/blog/item/d15b061b9120ae1d8618bfa4.html

http://www.cnblogs.com/allenlooplee/archive/2009/12/14/1623384.html

http://mianshi.fenzhi.com/post/1585.html

http://www.cntxk.com/CataNews/59/info8762.html