我最近将我的代码迁移到 Swift 4.我遇到了一个扩展问题,即

Declarations from extensions cannot be overridden yet

我已经阅读了多篇重新评论此问题的帖子.但他们都没有接受下面描述的情景：

@H_404_8@class BaseCell: UITableViewCell { //Some code here... } extension BaseCell { func isValid() -> String? { //Some code here... } } class SampleCell: BaseCell { //Some code here... override func isValid() -> String? //ERROR..!!! { //Some code here... } }

根据Apple的说法,

Extensions can add new functionality to a type,but they cannot override existing functionality.

但在上面的场景中,我没有在扩展中覆盖方法isValid().它在SampleCell类定义本身中被重写.不过,它正在给出错误.