Swift:覆盖也是父类属性类的子类的子类属性

Question

这似乎是一个令人困惑的问题，但实际上非常简单。我想做这样的事情，但 Swift 不允许这样做:

class A {}
class B : A {}
class C {
    var prop: A?
}
class D : C {
    override var prop : B?
}

Answer 1

取自here :

Overriding Property Getters and Setters

You can provide a custom getter (and setter, if appropriate) to override any inherited property, regardless of whether the inherited property is implemented as a stored or computed property at source. The stored or computed nature of an inherited property is not known by a subclass—it only knows that the inherited property has a certain name and type. You must always state both the name and the type of the property you are overriding, to enable the compiler to check that your override matches a superclass property with the same name and type.

看来你不能那样做。