using System;

using System.Linq;

using System.Collections.Generic;

using System.Text.Json;

public class Program

{

    public static void Main()

    {

        List<MyBaseClass> some = [new WithoutName(), new WithoutName(), new WithName(){Name = "Alphonso"}, new WithNameAndNumber(){Name = "Betrand", Number = 42}];

        Console.WriteLine("OfType<T> :");

        Console.WriteLine(JsonSerializer.Serialize(some.OfType<IHasName>()));

        Console.WriteLine("Where IsAssignableTo:");

        Console.WriteLine(JsonSerializer.Serialize(some.Where(x => x.GetType().IsAssignableTo(typeof(IHasName))).Select(x => (IHasName)x)));

        Console.WriteLine("Where 'is':");

        Console.WriteLine(JsonSerializer.Serialize(some.Where(x => x is IHasName).Select(x => (IHasName)x)));

        Console.WriteLine("Filter + Visitor");

        foreach(var item in some.Where(x => x is IHasName))

            item.Visit(x => x.Dump());

        Console.WriteLine("Visitor without Filter");

        foreach(var item in some)

            item.Visit(x => x.Dump());

        Console.WriteLine("Filter and cast");

        var listOfWithName = some.OfType<WithName>().ToList();

        Console.WriteLine(listOfWithName.GetType().Name);

        listOfWithName.Dump();

    }

}

​

public abstract class MyBaseClass

{

    public virtual void Visit(Action<IHasName> visitor){

        //NOP

    }

}

​

public interface IHasName 

{

    string Name {get;}

}

​

public sealed class WithName : MyBaseClass, IHasName

{

    public required string Name {get; init;}

    public override void Visit(Action<IHasName> visitor){

        visitor(this);

    }

}

public sealed class WithNameAndNumber : MyBaseClass, IHasName

{

    public required string Name {get; init;}

    public required int Number {get; init;}

    public override void Visit(Action<IHasName> visitor){

        visitor(this);

    }

}                                 

​

public sealed class WithoutName : MyBaseClass

{

}