swift factory for decodable type to one of possible results

Question

Note: saw this question but doesn't seem to resolve the issue: Swift Dynamically choose Codable struct for JSON field value based on response type

I don't know the runtime type before hand since decoding from a network call response. So currently I am attempting to decode in a try/catch one after another, but I am looking for a more concise way to do that based on a common property which could be used for a theoretical "switch" to define the runtime type.

I know that they always have a field with a key which can be mapped to the final type so is there a trick to use here? I am thinking something along the lines of a union type holding one of the possible results. Here is the example code I have:

struct Result1: Codable {
  let resultType: String = "result1" // this is always the case in the JSON for this particular type of result
  ...
  let other fields which are unique to this type of result
}

struct Result2: Codable {
  let resultType: String = "result2" // always this field in the json for this result type
  ...
  let other fields which are unique to this type of result ...
}

... Lot's of other types ...

struct ResultN: Codable { 
  let resultType: String = "resultN"
 ....
}


// Now how to decode the "either Result1 or Result2 or .... ResultN
let value = try JSONDecoder().decode(????.self, from: data) // don't know what type it will be yet 
if value is Result1 { ... handle this case ... }
if value is Result2 { ... handle this case ... }
....
if value is ResultN { ..... }

Perhaps decode to a general Json dictionary and from there map to the correct type?

Note:

Considering this mechanism (but lots of boiler plate):

let dict = try JSONSerialization.jsonObject(with: data) as? [String: Any]
switch dict["resultType"] {
  case "result1" : ... decode to res1
  ...
   case "resultN" : .... decode to resN

Answer 1

Using Dictionary of resultType to Codable maybe enough (JSON Decoding runs twice to get dict and value )

let map: Dictionary<String, Codable.Type> = [
    "result1": Result1.self,
    "result2": Result2.self,
　　　　　　　　// ...
    "resultN": ResultN.self
]

let codable = map[dict["resultType"]]
let value = try! JSONDecoder().decode(codable!, from: data)