问题描述

考虑这个枚举:

enum DataType {
    case One (data: Int)
    case Two (value: String)
}

Swift 有模式匹配来将枚举与关联值进行比较，如下所示:

Swift has pattern matching to compare an enum with associated values, like so:

let var1 = DataType.One(data: 123)
let var2 = DataType.One(data: 456)

if case DataType.One(data: _) = var2 {
    print ("var2 is DataType.One")
}

如何不将一个变量与一个枚举类型进行比较，而是比较两个变量的枚举类型?我看到了很多类似的问题，但没有一个专注于你有的情况两个变量.

How would one go about comparing not one variable against an enum type, but comparing the enum type of two variables? I saw a ton of similar questions, but none focused on the case where you have two variables.

我基本上想要的是:

if case var1 = var2 {
    print ("var1 is the same enum type as var2")
}

推荐答案

更新方法:

我认为对此没有本机支持.但是您可以通过定义自定义运算符来实现它(最好使用协议，但您也可以直接这样做).像这样的:

I think there's no native support for this. But you can achieve it by defining a custom operator (preferrably by using a protocol, but you can do it directly as well). Something like this:

protocol EnumTypeEquatable {
    static func ~=(lhs: Self, rhs: Self) -> Bool
}

extension DataType: EnumTypeEquatable {
    static func ~=(lhs: DataType, rhs: DataType) -> Bool {
        switch (lhs, rhs) {
        case (.one, .one), 
             (.two, .two): 
            return true
        default: 
            return false
        }
    }
}

然后像这样使用它:

let isTypeEqual = DataType.One(value: 1) ~= DataType.One(value: 2)
print (isTypeEqual) // true

旧方法:

protocol EnumTypeEquatable {
    var enumCaseIdentifier: String { get }
}

extension DataType: EnumTypeEquatable {
    var enumCaseIdentifier: String {
        switch self {
        case .one: return "ONE"
        case .two: return "TWO"
        }
    }
}

func ~=<T>(lhs: T, rhs: T) -> Bool where T: EnumTypeEquatable {
    return lhs.enumCaseIdentifier == rhs.enumCaseIdentifier
}

旧版本依赖于运行时，可能会提供默认的 enumCaseIdentifier 实现，具体取决于不推荐的 String(describing: self).(因为 String(describing: self) 正在使用 CustromStringConvertible 协议并且可以更改)

The older version depends on Runtime and might be provided with default enumCaseIdentifier implementation depending on String(describing: self) which is not recommended. (since String(describing: self) is working with CustromStringConvertible protocol and can be altered)

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