覆盖Swift中的存储属性 [英] Overriding a stored property in Swift

问题描述

我注意到编译器不允许我用另一个存储值覆盖存储的属性（这似乎很奇怪）：

I noticed that the compiler won't let me override a stored property with another stored value (which seems odd):

class Jedi {
    var lightSaberColor = "Blue"
}


class Sith: Jedi {
    override var lightSaberColor = "Red" // Cannot override with a stored property lightSaberColor
}

然而，我被允许这样做计算属性：

However, I'm allowed to do this with a computed property:

class Jedi {
    let lightSaberColor = "Blue"
}


class Sith: Jedi {
    override var lightSaberColor : String{return "Red"}

}

为什么我不允许给它另一个值？

Why am I not allowed to give it another value?

为什么要覆盖存储的属性憎恶和计算一个犹太人？他们在想什么？

Why is overriding with a stored property an abomination and doing it with a computed one kosher? What where they thinking?

推荐答案

为什么我不允许给它另一个值？

Why am I not allowed to just give it another value?

绝对允许您为继承的属性赋予不同的值。如果在获取该初始值的构造函数中初始化该属性，并从派生类传递不同的值，则可以执行此操作：

You are definitely allowed to give an inherited property a different value. You can do it if you initialize the property in a constructor that takes that initial value, and pass a different value from the derived class:

class Jedi {
    // I made lightSaberColor read-only; you can make it writable if you prefer.
    let lightSaberColor : String
    init(_ lsc : String = "Blue") {
        lightSaberColor = lsc;
    }
}

class Sith : Jedi {
    init() {
        super.init("Red")
    }
}

let j1 = Jedi()
let j2 = Sith()

println(j1.lightSaberColor)
println(j2.lightSaberColor)

覆盖一个属性与给它一个新值不同 - 它更像是给一个一个不同的属性。事实上，当你重写计算属性时会发生这种情况：计算基类中属性的代码是替换由代码计算派生类中该属性的覆盖。

Overriding a property is not the same as giving it a new value - it is more like giving a class a different property. In fact, that is what happens when you override a computed property: the code that computes the property in the base class is replaced by code that computes the override for that property in the derived class.

[是否]可以覆盖实际的存储属性，即 lightSaberColor 还有其他的行为？

除了观察者之外，存储的属性没有行为，因此实际上没有什么可以覆盖。通过上述机制可以赋予财产不同的价值。这正是问题中的示例试图用不同的语法实现的。

Apart from observers, stored properties do not have behavior, so there is really nothing there to override. Giving the property a different value is possible through the mechanism described above. This does exactly what the example in the question is trying to achieve, with a different syntax.

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