Cast Any to RawRepresentable where RawValue == String - ios

Question

I am trying to encode data. For the sake of the example I'll use JSON encoding even though there are other solutions for this out there.
I would like to handle enums that are backed by String or an Int as if they were simply String and Int:
struct UnhandledValueError: Error {}
enum Foo: String {
case bar
}
func encode(_ data: Any?) throws -> String {
guard let data = data else {
return "null"
}
if let string = data as? String {
return "\"\(string)\""
}
if let int = data as? Int {
return String(int)
}
// represent String and Int based enums there
if let array = data as? [Any?] {
return try "[\(array.map({ try encode($0) }).joined(separator: ","))]"
}
if let dict = data as? [String: Any?] {
return try "{\(dict.map({ "\"\($0.key)\": \(try encode($0.value))" }).joined(separator: ","))}"
}
throw UnhandledValueError()
}
let value: Any? = ["foo": Foo.bar]
try encode(value)
Because RawRepresentable is a generic protocol I don't think I can do either
if let value = data as? RawRepresentable
or
if let value = data as? RawRepresentable where RawValue == String
How can I access the raw value (as Any?) from an object that might be RawRepresentable ?

Answer 1

You can create a generic method and constrain its type to RawRepresentable where its RawValue conform to LosslessStringConvertible:
func encode<T>(object: T) -> String where T: RawRepresentable, T.RawValue: LosslessStringConvertible {
.init(object.rawValue)
}
Playground testing:
enum IntEnum: Int {
case a = 1, b, c
}
enum StringEnum: String {
case a, b , c
}
let int: IntEnum = .c
let string: StringEnum = .c
encode(object: int) // "3"
encode(object: string) // "c"