本文介绍了元组“上转”在Swift的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

如果我有一个签名(String,Bool)的元组我不能把它转换为(String,Any)。编译器说:

If I have a tuple with signature (String, Bool) I cannot cast it to (String, Any). The compiler says:

但这应该可以工作,因为 Bool 可以安全地转换为任何。如果你这样做,几乎相同的错误抛出:

But this should work since Bool can be casted safely to Any with as. Almost the same error gets thrown if you do something like that:

let any: Any = ("String", true)
any as! (String, Any) // error
any as! (String, Bool) // obviously succeeds

错误:

那么有什么解决方法,特别是对于第二种情况?因为你甚至不能将任何转换到任何可以分别投射元素的任何元组(Any,Any) p>

So is there any workaround especially for the second scenario? Because you cannot even cast Any to any tuple (Any, Any) where you could cast the elements separately.

推荐答案

元组不能被转换,即使它们包含的类型也可以。例如:

Tuples cannot be cast, even if the types they contain can. For example:

let nums = (1, 5, 9)
let doubleNums = nums as (Double, Double, Double) //fails

但是:

let nums : (Double, Double, Double) = (1, 5, 9) //succeeds

您的情况下的解决方法是转换单个元素,而不是元组本身:

The workaround in your case is to cast the individual element, not the Tuple itself:

let tuple = ("String", true)
let anyTuple = (tuple.0, tuple.1 as Any)
// anyTuple is (String, Any)

这是原因之一注释:

我认为这是一个实现限制,因为元组是复合类型像函数。同样,您不能创建元组的扩展(例如 extension(String,Bool){...} )。

I think this is an implementation limitation because Tuples are compound types like functions. Similarly, you cannot create extensions of Tuples (e.g. extension (String, Bool) { … }).

如果你实际上使用返回(String,Any)的API,请尝试将其改为使用类或结构。但如果您无权改进API,您可以在第二个元素的类型上切换

If you're actually working with an API that returns (String, Any), try to change it to use a class or struct. But if you're powerless to improve the API, you can switch on the second element's type:

let tuple : (String, Any) = ("string", true)

switch tuple.1 {

case let x as Bool:
    print("It's a Bool")
    let boolTuple = (tuple.0, tuple.1 as! Bool)

case let x as Double:
    print("It's a Double")
    let doubleTuple = (tuple.0, tuple.1 as! Double)

case let x as NSDateFormatter:
    print("It's an NSDateFormatter")
    let dateFormatterTuple = (tuple.0, tuple.1 as! NSDateFormatter)

default:
    print("Unsupported type")
}

如果API返回 Any 保证(String,Any),你运气不好。

If the API returns Any and the tuple isn't guaranteed to be (String, Any), you're out of luck.

这篇关于元组“上转”在Swift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!

08-14 09:19