如何要求在 Swift 协议中定义枚举

Question

是否可以让协议要求定义枚举？

//trying to do this
protocol JSONEncodable {
    enum PropertyName // Type not allowed here
    func valueForProperty(propertyName:PropertyName) -> Any
}

//which would be implemented like this
struct Person : JSONEncodable {
    var firstName : String
    var lastName : String

    enum PropertyName {
        case FirstName
        case LastName
        func allValues() {
            return [Person.PropertyName.FirstName, Person.PropertyName.LastName]
        }
        func stringValue() {
            return "\(self)"
        }
    }
    func valueForProperty(propertyName:PropertyName) -> Any {
        switch propertyName {

        case .FirstName:
            return firstName

        case .LastName:
            return lastName
        }
    }
}

//so that I could do something like this
extension JSONEncodable {

    func JSONObject() -> [String:AnyObject] {
        var dictionary = [String:AnyObject]()
        for propertyName in PropertyName.allValues {
            let value = valueForProperty(propertyName)

            if let valueObject = value as? AnyObject {
                dictionary[propertyName.stringValue()] = valueObject

            }else if let valueObject = value as? JSONEncodable {
                dictionary[propertyName.stringValue()] = valueObject.JSONObject()
            }

        }
        return dictionary
    }
}

Answer 1

协议可以有 associatedtypes 这只需要在任何子类中遵守：

enum MyEnum: String {
    case foo
    case bar
}

protocol RequiresEnum {
    associatedtype SomeEnumType: RawRepresentable where SomeEnumType.RawValue: StringProtocol

    func doSomethingWithEnum(someEnumType: SomeEnumType)
}

class MyRequiresEnum: RequiresEnum {
    typealias SomeEnumType = MyEnum

    func doSomethingWithEnum(someEnumType: SomeEnumType) {
        switch someEnumType {
        case .foo:
            print("foo")
        case .bar:
            print("bar")
        }
    }
}

let mre = MyRequiresEnum()
mre.doSomethingWithEnum(.bar)

编辑：associatedtype必须遵守

Answer 2

我认为您可以使用符合 RawRepresentable

的 associatedtype

这是一个例子：

protocol SomeProtocol {
    associatedtype SomeType: RawRepresentable
}

如果您需要指定 RawRepresentable 的类型，例如 String，您可以这样做：

protocol SomeProtocol {
    associatedtype SomeType: RawRepresentable where SomeType.RawValue: StringProtocol
}

现在，如果您尝试使用具有 String 作为 RawRepresentable 的 enum 以外的任何其他方式来实现协议，您将遇到编译器错误。希望对你有帮助。

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