MultiPayloadDecoder.swift

// To decode a json where the type to decode is in the json itself like:
// [{ "type": "foo", "payload": { "word": "hello" "push_id": 3711282988, "size": 1, } }, { "type": "bar", "payload": { "size": 1, "radious": 0.5 } }]


struct FooPayload: Codable {
    var word: String
    var push_id: Int
	var size: Int
}

struct BarPayload: Codable {
    var size: Int
	var radious: Double
}

struct Foo {
    var type: String
    var payload: Payload?
    enum CodingKeys : CodingKey {
        case type, payload
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        type = try values.decode(String.self, forKey: .type)
        swith type {
        case "foo":
            payload = values.decode(FooPayload.self, forKey: .payload)
        case "bar":
            payload = values.decode(BarPayload.self, forKey: .payload)
        default:
            payload = nil
        }
    }
}