获取类名类方法中 用self
对象方法object_getClass(self)==self.dynamicType 真正的类名
参考文章
http://www.jianshu.com/p/b46653d7a861
http://stackoverflow.com/questions/24403718/swift-equivalent-objective-c-runtime-class
http://stackoverflow.com/questions/24049673/swift-class-introspection-generics