Swift泛型类型强制转换 [英] Swift generic type cast

问题描述

我有一个泛型类，我有一个泛型类型的数组。不，我想根据数组中的类进行一些操作。我有2个班级：人与家（无继承）。但是这段代码不起作用：

  let allValues = [T]（）
如果allValues [0]是Person {
 let values =（allValues as [Person]）
} 
  

但是这不起作用，因为 T与'Person'不一样。我需要做什么？感谢您的帮助。

strong>：这种问题应该使用协议解决。

然而，您可以使用此语法执行演员阵容：

 让values = allValues as Any作为[Person] 
  

现在我看到两个问题：

1. 您的 IF 会因为您的数组 allValues 包含0
   元素，并且您正在访问第一个元素（不存在）。



2. allValues可以在第一个元素处具有Person，在第二个位置还有
   的东西。

   
   
   

   示例
   
   

   class LifeForm {}

   p>
   
   

   类Person：LifeForm {}

   
   
   

   T等于LifeForm。

我认为以下版本更安全，因为您直接评估T类型。

  class Things< T> {
 func doSomething（）{
 let allValues = [T]（）
 //填充allValues .... 
如果T.self是Person.Type {
 println（Person of List）
让values = allValues as Any作为[Person] 
} 
} 
} 
  

重要提示：我提供此代码仅用于显示语法。我不喜欢这个abborach（再次，一个协议会更好），因为这个类包含特定于Person的逻辑。
理想情况 对 Person 应该一无所知，因为事物是泛型类。

I have a generic class where I have an array of generic types. No I want to do some operations based on the class in the array. I have 2 classes: Person and House (no Inheritance). But this code doesn't work:

let allValues = [T]()
if allValues[0] is Person { 
     let values = (allValues as [Person])
}

But this doesn't work as T is not identical to 'Person'. What do I have to do? Thanks for any help.

解决方案

I agree with Oliver Borchert and Airspeed Velocity: this kind of problem should be addressed using a protocol.

However you can perform the cast you asked about using this syntax:

let values = allValues as Any as [Person]

Now I see 2 problems:

1. Your IF will crash because your array allValues contains 0 elements and you are accessing the first one (that does not exist).

2. allValues could have a Person at the first element and something else at the second position. This makes dangerous a cast after having evaluated only the first element.

   Example

   class LifeForm {}

   class Person : LifeForm {}

   With T equals to LifeForm.

I think the following version is safer because you are directly evaluating the type T.

class Things<T>{
    func doSomething() {
        let allValues = [T]()
        // populate allValues....
        if T.self is Person.Type {
            println("List of Person")
            let values = allValues as Any as [Person]
        }
    }
}

Important: I provided this code just to show the syntax. I don't like this abborach (again, a Protocol would be better) because the class Things contains logic specific to Person. Ideally Things should know nothing about Person because Things is a generic class.

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