关于Swift中重写类属性的困惑 [英] Confusion Regarding Overriding Class Properties in Swift

问题描述

我已经阅读了Swift文档并在这里进行了搜索，但是我仍然不确定如何实现一个类层次结构，其中每个子类都为继承的静态属性设置自定义值.即:

I have read the Swift docs and searched here, but I still am not sure about how to implement a class hierarchy where each subclass sets custom value for an inherited static property; that is:

1. 基类定义了静态属性:所有实例共享相同的值.
2. 子类覆盖静态属性:所有实例共享相同的值，与基类的形式不同.

可以存储财产吗?

此外，我应该如何从实例方法(无论特定的类)中访问属性的值，并每次都获取正确的值?以下代码可以工作吗?

Also, How should I access the value of the property from within an instance method (regardless of the particular class), and get the correct value everytime? will the following code work?

class BaseClass 
{
    // To be overridden by subclasses:
    static var myStaticProperty = "Hello"

    func useTheStaticProperty()
    {
        // Should yield the value of the overridden property
        // when executed on instances of a subclass: 
        let propertyValue = self.dynamicType.myStaticProperty

        // (do something with the value)
    }  

推荐答案

您是如此接近，除了不能覆盖子类中的static属性，这就是.因此，您必须使用class属性，这意味着它必须是计算属性-Swift缺少存储的class属性.

You are so close to being there, except that you can't override a static property in a subclass — that is what it means to be static. So you'd have to use a class property, and that means it will have to be a computed property — Swift lacks stored class properties.

所以:

class ClassA {
    class var thing : String {return "A"}
    func doYourThing() {
        print(type(of:self).thing)
    }
}
class ClassB : ClassA {
    override class var thing : String {return "B"}
}

让我们对其进行测试:

ClassA().doYourThing() // A
ClassB().doYourThing() // B

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