using System;

using System.Text;

using System.IO;

using System.Xml;

using System.Xml.Serialization;

using System.Text.Json;

using System.Text.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var fooWithBar = new Foo() { Bar = new Bar() };

        Console.WriteLine(SerializeToXml(fooWithBar));

        Console.WriteLine();

        var fooWithPub = new Foo() { Bar = new Pub() };

        Console.WriteLine(SerializeToXml(fooWithPub));

        Console.WriteLine("----");

        Console.WriteLine(JsonSerializer.Serialize(fooWithBar));

        Console.WriteLine(JsonSerializer.Serialize(fooWithPub));

    }

    public static string SerializeToXml<T>(T tValue)

    {

        using var ms = new MemoryStream();

        using var xmlWriter = XmlWriter.Create(ms, new()

        {

            Encoding = Encoding.UTF8,

            Indent = true

        });

        XmlSerializer xmlSerializer = new(typeof(T));

        xmlSerializer.Serialize(xmlWriter, tValue);

        ms.Position = 0;

        return Encoding.UTF8.GetString(ms.ToArray());

    }

    public class Foo

    {

        [XmlElement("Bar", typeof(Bar))]

        [XmlElement("Pub", typeof(Pub))]

        public BaseBar Bar { get; set; }

    }

    [JsonDerivedType(typeof(Bar), typeDiscriminator: nameof(Bar))]

    [JsonDerivedType(typeof(Pub), typeDiscriminator: nameof(Pub))]

    public abstract class BaseBar

    {

        public abstract string Text { get; set; }

    }

    public class Bar : BaseBar

    {

        public override string Text { get; set; } = "I am a Bar";

    }

    public class Pub : BaseBar

    {

        public override string Text { get; set; } = "I am a Pub";

    }

}