扩展中的Swift覆盖函数 [英] Swift override function in extension

问题描述

如果我有一个类：

 类Spaceship< FuelType> {
函数prepareForLiftoff（）抛出{
 //开始倒计时！ 
 
 
 
 
 $ b我原本以为我可以覆盖 prepareForLiftoff 无需通过添加扩展来创建子类： 
 
 
 扩展Spaceship其中FuelType：CollectionType {
 func prepareForLiftoff（）throws {} 
} 
  
这段代码没有' t编译虽然，错误说无效重新声明的功能，这是有道理的。
 
 
 
 我的问题是：是否有重写某个特定类的函数？换句话说，我可以在某些情况下替换功能，例如上面的示例 FuelType：CollectionType 。如果没有，是否有任何其他的解决方法或方法来实现该行为（也许宣布另一个协议，idk）
 
 
 
现在我想到更多，我不得不说这是不可能的，因为什么是阻止某人重写任何标准库函数？ 解析方案

从文档：

扩展可以为类型添加新功能，但不能覆盖现有功能。

准确地说是什么扩展是允许做。

至于你的问题：

是否有重写某个类的函数

是的，它叫做子类。

If I have a class:

class Spaceship<FuelType> {
    function prepareForLiftoff() throws {
        //Start the countdown!
    }
}

I originally assumed that I would be able to override prepareForLiftoff without subclassing by adding an extension:

extension Spaceship where FuelType: CollectionType {
    func prepareForLiftoff() throws {}
} 

This code doesn't compile though, the error says invalid redeclaration of the function, which makes sense.

My question is: Is there anyway to override a function of a particular class? In other words can I replace the functionality under certain conditions like the example above where FuelType: CollectionType. If not, is there any other workaround or way to achieve that behavior (maybe declaring another protocol, idk)

Now that I think about it more, I would have to say that's not possible because what's to stop someone from overriding any of the standard library functions?

解决方案

From the documentation:

Extensions can add new functionality to a type, but they cannot override existing functionality.

The documentation lists carefully and precisely what an extension is allowed to do.

As to your question:

Is there anyway to override a function of a particular class

Yes, it's called subclassing.

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