using System;

using System.Text.Json.Serialization;

​

interface IBase {

    [JsonPropertyName("interface-magic")]

    int Magic {get;}

}

​

class DerivedFromInterface : IBase {

    public int Magic { get; init; }

}

​

​

abstract class AbsBase {

    [JsonPropertyName("abstract-magic")]

    abstract public int Magic {get; init; }

}

​

class DerivedFromAbstract : AbsBase {

    override public int Magic { get; init; }

}

​

public class Program

{

    public static void Main()

    {

        static void json<T>(T thing) {

            var ser = System.Text.Json.JsonSerializer.Serialize(thing);

            Console.WriteLine(ser);

        }

        var easygoing = new DerivedFromInterface() { Magic  = 5 };

        json(easygoing);

        json(easygoing as IBase);

        var uglee = new DerivedFromAbstract() { Magic = 93 };

        json(uglee);

        json(uglee as AbsBase);

    }

}