Comparing two enum variables regardless of their associated values

问题

Consider this enum:

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

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")
}

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.

What I basically want is:

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

回答1:

Updated approach:

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
        }
    }
}

And then use it like:

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

Old approach:

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
}

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)

回答2:

Just confirm to Equatable like below

extension DataType: Equatable {
    static func == (lhs: DataType, rhs: DataType) -> Bool {
        switch (lhs, rhs) {
        case (.One, .Two), (.Two, .One):
            return false
        case (.One, .One), (.Two, .Two):
            return true
        }
    }
}

If you don't want to implement Equatable just move content into instance method:

extension DataType{
    func isSame(_ other: DataType) -> Bool {
        switch (self, other) {
        case (.One, .Two), (.Two, .One):
            return false
        case (.One, .One), (.Two, .Two):
            return true
        }
    }
}

Use:

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

回答3:

This worked for me:

enum DataType {
    case one (data: Int)
    case two (value: String)
}

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

extension DataType: EnumTypeEquatable {
    static func sameType(lhs: DataType, rhs: DataType) -> Bool {
        if let caseLhs = Mirror(reflecting: lhs).children.first?.label, let caseRhs = Mirror(reflecting: rhs).children.first?.label {
            return (caseLhs == caseRhs)
        } else { return false }
    }
}

let isTypeEqual = DataType.sameType(lhs: .one(data: 1), rhs: .one(data: 2))
print (isTypeEqual) // true

来源：https://stackoverflow.com/questions/54402685/comparing-two-enum-variables-regardless-of-their-associated-values

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