swift - 从具有相同父类(super class)的多个类继承 - 解决方法

Question

以下情况:

class Sprite{ // has to be a class, not a protocol!
    func s(); // can not be changed
}
class Element: Sprite{
    // needs s(); for:
    func e();
}
class Wiggle: Sprite{
    // needs s(); for:
    func w();
}

我怎样才能实现这样的目标:

class Button: Wiggle{
    // needs s();
    // needs w();
}
class Cursor: Element, Wiggle{
    // needs s();
    // needs w();
    // needs e();
}
class Pointer: Element{
    // needs w();
    // needs e();
}

这不起作用，因为 Cursor Wiggle 和 Element 都继承自 Sprite。

因此我正在考虑使用扩展方法，例如:

class Button:Sprite{
    // needs s();
    // needs w();
}
class Cursor: Element{
    // needs s();
    // needs w();
    // needs e();
}
class Pointer: Element{
    // needs w();
    // needs e();
}

extension Button, Cursor { // or similar to make w() available in Button & Cursor
    // using s() for:
    // func w();
}

如何一步扩展 Button 和 Cursor？

Answer 1

您可以将 w() 放入其自己的协议(protocol)中，例如Wable，Button 和 Cursor 符合。为 Wable 提供 w() 的默认实现。由于 w() 依赖于 s()，因此您必须对扩展施加约束，使其仅适用于从 Sprite 派生的符合类型>(s() 的“源”)。

class Button: Sprite, Wable {
    // needs s(); inherited from Sprite
    // needs w(); inherited from Wable
}

class Cursor: Element, Wable {
    // needs s(); inherited from Sprite
    // needs w(); inherited from Wable
    // needs e(); inherited from Element
}

class Pointer: Element, Wable  {
    // needs w(); inherited from Wable
    // needs e(); inherited from Element
}

protocol Wable {
    func W()
}

extension Wable where Self : Sprite {
    func W() {
        print("foo")
    }
}