Runtime

    id objc =  [NSObject alloc];

   objc_msgSend(objc_getClass("NSObject"), sel_registerName("alloc"))

   objc = [objc init];

      objc_msgSend(objc, sel_registerName("init"))

         id objc = ((NSObject *(*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("NSObject"), sel_registerName("alloc"));

         objc = ((id (*)(id, SEL))(void *)objc_msgSend)((id)objc, sel_registerName("init"));

Runtime

原文：http://www.cnblogs.com/liuzhenjie/p/5243620.html