codableProtocols.swift

import Foundation
import UIKit

let json = """
[{
"first_name": "Shakti",
"last_name": "prakash",
"age":25,
"address":"Cuttack,Odisha,India"
},
{
"first_name": "Soumen",
"last_name": "Mohanty",
"age":"25",
"address":null
}]
"""

let jsonData = Data(json.utf8)

enum VariacType:Codable{
    
    func encode(to encoder: Encoder) throws {
        
    }
    
    case int(Int)
    case string(String)
    init(from decoder: Decoder) throws {
        if let intValue = try? decoder.singleValueContainer().decode(Int.self)  {
            self = .int(intValue)
            return
        }
        if let stringValue = try? decoder.singleValueContainer().decode(String.self){
            self = .string(stringValue)
            return
        }
        throw VariacError.missingValue
    }
    
    
    enum VariacError: Error {
        case missingValue
    }
}

extension VariacType {
    var Value:String {
        switch self {
        case .int(let intvalue):
            return String(intvalue)
        case .string(let stringValue):
            return stringValue
        }
    }
    
}

struct Person: Codable{
    var firstName: String
    var lastName: String
    var age: VariacType
    var  address: String
    private enum CodingKeys: String, CodingKey{
        case firstName = "first_name"
        case lastName = "last_name"
        case age
        case address
        
    }
    
    func encode(to Encoder: Encoder) throws{
        
    }
    init(from decoder: Decoder) throws{
        let container = try decoder.container(keyedBy: CodingKeys.self)
           firstName = try container.decode(String.self, forKey: .firstName)
            lastName = try container.decode(String.self, forKey: .lastName)
           // age = try container.decode(VariacType.self, forKey: .age)
            age = (try container.decodeIfPresent(VariacType.self, forKey: .age)) ?? VariacType.int(0)
          address =
            (try container.decodeIfPresent(String.self, forKey: .address)) ?? "Unknown Address"
    }
    
}



let decoder = JSONDecoder()

do {
   let response = try decoder.decode([Person].self, from: jsonData)
    print(response[0].age.Value)
} catch let error  {
    print("Parsing Failed \(error.localizedDescription)")
}