Swift Cast泛型类型 [英] Swift Cast Generics Type

问题描述

我试图将泛型类型强制转换为其超类。

I'm trying to cast a generic type to its super class.

class Foo : NSObject {
}
class Test<T> {
    let value: T
    init(_ value: T) {
        self.value = value
    }
}

let c = Test(Foo())
let v = c as Test<AnyObject>

但在行上

let v = c as Test<AnyObject>

我得到'Foo'不等于'AnyObject'

I get 'Foo' is not identical to 'AnyObject'

我可以用内置的数组

let array1 = [Foo(), Foo()]
let array2 = array1 as [AnyObject]

推荐答案

数组在Swift中是特殊的，可以有这种行为。

Arrays are special-cased in Swift to be able to have this behaviour. You won't be able to replicate it with your own classes, unfortunately.

为了得到类似的行为，你可以给你的类型另一个 init 方法：

To get similar behaviour, you could give your type another init method:

class Test<T> {
    let value: T
    init(_ value: T) {
        self.value = value
    }

    init<U>(other: Test<U>) {
        // in Swift 1.2 you will need as! here
        self.value = other.value as T
    }
}

let c = Test(Foo())
let v = Test<AnyObject>(other: c)  // this will work ok

注意，这是不安全的将在运行时断言）在您想要转换为不兼容类型（和备选，一个failable初始值，也将有并发症）

Note though that this is unsafe (i.e. will assert at runtime) in cases where you want to convert to an incompatible type (and the alternative, a failable initializer, will also have complications)

这篇关于Swift Cast泛型类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！