您可以严格使用泛型类型，也可以给一个参数多于一种类型吗? [英] Can you Strict Generic types or give one parameter more than one type ?

问题描述

例如，我想指定一个可能为Integer或String的类型，并将其用作func中的特殊类型，我尝试了typealias 但是它不能解决这种情况，因为类型别名不能具有or参数，因为它仅使用&，因此请考虑以下情况.

For example i want to specify a type that might be Integer or String and use it as special type in func i tried typealias but it wont solve the case because typealiases can't have or arguments as its only uses & therefore consider the case below.

typealias alis = StringProtocol & Numeric


func foo <T: alis> (vee: T) -> T{
// do something
    return vee
}

我希望此函子接受(Int或String)而不是其他任何参数(<T>)的参数类型

i want this func to accept a parameter type of either ( Int or String ) not anything else (<T>),

如您所见，我尝试使用typealias并且没有编译错误.

as you can see i tried with typealias and i have no compile error.

但是，尝试使用该功能将导致这些错误.

however trying to use the function will lead to these errors.

foo(vee: 1) //Argument type 'Int' does not conform to expected type 'StringProtocol'

还有

foo(vee: "v") //Argument type 'String' does not conform to expected type 'Numeric'

这可以迅速实现吗?如果是这样的话.

is this achievable with swift ? if so how.

推荐答案

让我们假设您可以使用OR运算符组合协议，那么对于?

Let's suppose that you could use a OR operator to combine protocols, what would you be able to do with something of type (Int | String)?

并不是所有您可以对Int进行的操作都可以在(Int | String)上完成，因为它可能是一个潜在的字符串.同样，并不是您可以对(Int | String)进行的所有操作都可以在(Int | String)上完成，因为从根本上说，它可能是Int.

Not everything you can do to an Int can be done on (Int | String), because it might be a string underlyingly. Similarly, not everything you can do to an String can be done on (Int | String), because it might be a Int underlyingly.

现在您可能会说:啊.我知道Int和String都具有description属性.我应该能够使用类型为(Int | String)的变量访问description."

Now you might say "Ah. I know that Int and String both have a description property. I should be able to access description on a variable of type (Int | String)."

在这种情况下，您可以自己创建一个这样的协议，并且仅使Int和String符合该协议:

Well, in that case, you can just create such a protocol yourself and only have Int and String conform to it:

protocol IntOrString {
    var description: String { get }
}

extension Int : IntOrString {}
extension String : IntOrString {}

(请注意，在CustomStringConvertible中已经定义了description.为争辩起见，假设它不存在.)

(Note that description is already defined in CustomStringConvertible. For the sake of argument, imagine that does not exist.)

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