using System;
using System.Collections.Generic;
 
public /*abstract*/ class BaseDBObject
{
	public BaseObjectsList<BaseDBObject> ParentList { get; set; }
}
 
public class BaseObjectsList<T> /* : IEnumerable<T> */ where T : BaseDBObject, new()
{
	public List<T> ObjectsList { get; set; } = new List<T>();
 
	public void Fill()
    {
        ObjectsList.Clear();
        ObjectsList.Add(new T());
    }
}
 
public class Smth : BaseDBObject
{
}
 
public class Test
{
	public static void Main()
	{
		var list = new BaseObjectsList<Smth>();
		list.Fill();
	}
}

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