import UIKit

var json = """
{
  "type": "int",
  "value": 1
}
"""

struct MyString: Codable {
    let value: String
    enum keys: CodingKey {
        case value
    }
}
struct MyInt: Codable {
    let value: Int
}

struct TypeContainer: Decodable {
    let type: SupportedType
    enum SupportedType: String, Codable {
        case string
        case int
    }
}

do {
    let typeContainer = try JSONDecoder().decode(TypeContainer.self, from: json.data(using: .utf8)!)

    switch typeContainer.type {
    case .string:
        let string = try JSONDecoder().decode(MyString.self, from: json.data(using: .utf8)!)
        print("string value: \(string.value)")
    case .int:
        let int = try JSONDecoder().decode(MyInt.self, from: json.data(using: .utf8)!)
        print("int value: \(int.value)")
    }
} catch {
    print(error)
}