using System;

using System.Collections.Generic;

using System.Linq;

​

namespace ConsoleTests

{

    public abstract class EntityAbs

    {

        //Save itself in a Database

        public abstract int SaveEntity();

    }

    public abstract class ListEntitiesAbs<T> where T : EntityAbs

    {

        protected List<T> InnerList;

​

        //Save each values in a Database

        public virtual int SaveEntities()

        {

            return InnerList.Sum(entity => entity.SaveEntity());

        }

    }

​

    public class Item : EntityAbs

    {

        public override int SaveEntity()

        {

            throw new NotImplementedException();

            // Implements here how I save it

        }

    }

    public class Items : ListEntitiesAbs<Item>

    {

        // Has specific class stuff in it

    }

​

    public class ItemB : EntityAbs

    {

        public override int SaveEntity()

        {

            throw new NotImplementedException();

            // Implements here how I save it

        }

    }

    public class ItemsB : ListEntitiesAbs<ItemB>

    {

        // Has specific class stuff in it

    }

​

    public class ItemC : EntityAbs

    {

        public override int SaveEntity()

        {

            throw new NotImplementedException();

            // Implements here how I save it

        }

    }

    public class ItemsC : ListEntitiesAbs<ItemC>

    {

        // Has specific class stuff in it

    }

​

    public class AnAnotherClass

    {

        public int Save<T>(params ListEntitiesAbs<T>[] lists) where T : EntityAbs

        {

            for (int i = 0; i < lists.Length; i++)

                lists[i].SaveEntities();

​

            return 1;

        }

    }

    class Program

    {

        static void Main(string[] args)

        {

            AnAnotherClass c = new AnAnotherClass();

            Items items = new Items();

            ItemsB items2 = new ItemsB();

            ItemsC items3 = new ItemsC();

​

            int result = c.Save( 

                items, 

                items2, 

                items3);

            // ERROR CS0411

​

            int result2 = c.Save<EntityAbs>(

                items,

                items2,

                items3);

            // ERROR CS1503

​

        }

    }

}

​

​

​