How to access associate enum in generic way in swift - swift

Question

I am trying to understand swift enum and for that, I decided to create a data source using an associated enum. Now I am not sure if my question line is correct or not but I'll try to explain what exactly I am trying to do here.
Struct SampleClass {
enum Country: String {
case US(cityList: ChianCityList)
case Chian(cityList: USCityList)
}
enum ChianCityList {
case Bijing
case Shanghai
static var allCases = [.Bijing, .Shanghai]
}
enum USCityList {
case NewYork
case LA
static var allCases = [.NewYork, .LA]
var isCaptial:Bool
}
var country: Country
var allCityList: [?] {
switch self.conuntry {
case Chian
return CityList.allCases
case US
return USCityList.allCases
}
init(country: Country)
{
self.country = Country
}
}
Now I don't know what would be the return type of var 'allCityList'. I want it to be generic. secondly, I don't want to call 'allCases' for each enum. Is there anyway to make it more generic? This is just a simple example there is a lot of scenarios like this. Like 'isCaptial'. How could i make it more generic so that based on the country I can found out?

Answer 1

Currently, USCityList and ChinaCityList are two separate types. If you return one type you can‘t return the other. You have two options.
enum ChianCityList {
case Bijing
case Shanghai
static var allCases = [.Bijing, .Shanghai]
}
enum USCityList {
case NewYork
case LA
static var allCases = [.NewYork, .LA]
var isCaptial:Bool
}
Option 1: Convert the one you currently return to the same type and make said type as the return type
Example:
enum ChianCityList: String, CaseIterable {
case Bijing
case Shanghai
}
enum USCityList: String, CaseIterable {
case NewYork
case LA
var isCaptial:Bool
}
extension CaseIterable {
var allCasesToStrings: [String] {
return allCases.map{ String(describing: $0) }
}
var allCityList: [String] {
switch self.conuntry {
case Chian
return CityList.allCasesToStrings
case US
return USCityList.allCasesToStrings
}
Option 2: Make both types conform to the same protocol, then return an instance of said protocol.
Example:
protocol CityList {
var cityList: [String] { get }
Var capitalCity: String { get }
}
// Have both implement the protocol
var allCityList: CityList {
switch self.conuntry {
case Chian
return CityList.cityList
case US
return USCityList.cityList
}

Answer 2

For your example, I wouldn't use enums. This is because you want to store additional information about the cities (like if it's a capital city). Instead, I would use a struct called City that encapsulates all your information. Then you can have a variable chinaCities and usCities that is an array of all its respective cities.
If you truly wanted to force the use of enums, I would create one giant enum called City and store an array of Citys into two separate variables to differentiate their locations.
enum City: String {
case beijing = "beijing"
case newYork = "new york"
}
Of course, if you do this, you'll also have to do extra work to keep track of whether a city is a variable. One way you can achieve this is by having a function that takes in a City enum and returns true or false depending on whether it is a capital.
As a side note, I just wanted to point out that you spelled China and Beijing wrong. Hope this helps!