小编Jon*_*esy的帖子

以下代码抛出错误

protocol WhatA: AnyObject {
    func doThat()
}

protocol WhatB: WhatA {
    func doThis()
}

class SomethingA {
    weak var delegate: WhatA?
}

class SomethingB: SomethingA {
    weak var delegate: WhatB?
}

类型为“ WhatB？”的属性“委托” 无法覆盖类型为“ WhatA？”的属性

UIKit在以下方面没有问题

open class UIScrollView : UIView, NSCoding, UIFocusItemScrollableContainer {

    weak open var delegate: UIScrollViewDelegate?

}

open class UITableView : UIScrollView, NSCoding, UIDataSourceTranslating {

    weak open var delegate: UITableViewDelegate?

}

为什么这在UIKit中起作用？这个问题的公认答案表明这是不可能的。