How to require an enum be defined in Swift Protocol

Question

Is it possible to have a Protocol require that an enum be defined?

//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

Protocols can have associatedtypes which would just need to be adhered to in any subclass:

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) 

Edit: The associatedtype must be adhered to

Answer 2

I think you can do it with an associatedtype that adheres to RawRepresentable

Here's an example:

protocol SomeProtocol {     associatedtype SomeType: RawRepresentable } 

If you need to specify the type of RawRepresentable like String for example, you can do that:

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

Now you'll have a compiler error if you try to implement the protocol with anything else than an enum that has String as RawRepresentable. I hope it helps.