using System;

using System.Collections;

using System.Collections.Generic;

public class FooList : IEnumerable<Type> {

  private HashSet<Type> m_Types = new HashSet<Type>();

​

  public bool Add(object value) => value is null

    ? false

    : m_Types.Add(value.GetType());

​

  public IEnumerator<Type> GetEnumerator() => m_Types.GetEnumerator();

​

  IEnumerator IEnumerable.GetEnumerator() => m_Types.GetEnumerator();

}

​

public class FooA {}

public class FooB {}

​

public class Program {

  public static void Main() {

    FooA fooA = new FooA();   

    FooB fooB = new FooB();

    FooB anotherFooB = new FooB();

​

    FooList list = new FooList();

    list.Add(fooA);

    list.Add(fooB);

list.Add(anotherFooB);

​

foreach(var item in list)

{

  Console.WriteLine(item);

}

  }

}