using System;

using System.Collections.Generic;

​

#nullable enable                    

​

public class Program

{

    public static void Main()

    {

        var request = RequestFactory.CreateRequest(RequestType.Foo);

        // No way to get at request.FooThing here without type testing/downcasting

    }

}

​

public static class RequestFactory 

{

    public static IRequest CreateRequest(RequestType requestType)

    {

        return requestType switch 

        {

                RequestType.Foo => new FooRequest(),

                RequestType.Bar => new BarRequest()

        };

    }

}

​

public interface IRequest 

{

    object CommonThing {get;set;}

}

​

public class FooRequest : IRequest 

{

    public object CommonThing {get;set;}

    public object FooThing {get;set;}

}

​

public class BarRequest : IRequest 

{

    public object CommonThing {get;set;}

    public object BarThing {get;set;}

}

​

public enum RequestType

{

    Foo,

    Bar

}