关于内存默认
*/
Class Hero = objc_allocateClassPair([NSObject class], "Hero", 0);
class_addMethod...class_addIvar(Hero, "W", sizeof(NSString *), 0, "@");//添加成员变量
//添加属性实现setter getter方法
class_addMethod...(Hero, @selector(setW:), (IMP)setW, "v@:@");
class_addMethod(Hero, @selector(getW), (IMP)getW, "@