using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

​

​

public class Program

{

    public static void Main()

    {

            var results = new List<object>();

            var l = new ListWrapper();

            IList<object> li = l;

            Console.WriteLine("Call via foreach direct");

            foreach(var o in l)

            {

                results.Add(0);

            }

​

            Console.WriteLine("Call via LINQ direct");

            results.AddRange(l.Select(o => o));

​

            Console.WriteLine("Call via foreach interface");

            foreach (var o in li)

            {

                results.Add(0);

            }

​

            Console.WriteLine("Call via LINQ interface");

            results.AddRange(li.Select(o => o));

    }

    public class ListWrapper : IEnumerable<object>, IList<object>

        {

            List<object> _list = new List<object>() { "1", "2", "3" };

​

​

            public List<object>.Enumerator GetEnumerator()

            {

                Console.WriteLine("direct method call (no boxing)");

                Console.WriteLine();

                return _list.GetEnumerator();

            }

​

            #region IEnumerable

​

            IEnumerator<object> IEnumerable<object>.GetEnumerator()

            {

                Console.WriteLine("interface call (with boxing)");

                Console.WriteLine();

​

                return ((IEnumerable<object>)_list).GetEnumerator();

            }

​

            IEnumerator IEnumerable.GetEnumerator()

            {

                Console.WriteLine("interface call (with boxing)");

                Console.WriteLine();

                return ((IEnumerable<object>)_list).GetEnumerator();

            }

​

            #endregion IEnumerable

​

            #region IList

​

            public object this[int index] { get => ((IList<object>)_list)[index]; set => ((IList<object>)_list)[index] = value; }

​

            public int Count => ((IList<object>)_list).Count;

​

            public bool IsReadOnly => ((IList<object>)_list).IsReadOnly;

​

            public void Add(object item)

            {

                ((IList<object>)_list).Add(item);

            }

​

            public void Clear()

            {

                ((IList<object>)_list).Clear();

            }

​

            public bool Contains(object item)

            {

                return ((IList<object>)_list).Contains(item);

            }

​

            public void CopyTo(object[] array, int arrayIndex)

            {

                ((IList<object>)_list).CopyTo(array, arrayIndex);

            }

​

            public int IndexOf(object item)

            {

                return ((IList<object>)_list).IndexOf(item);

            }

​

            public void Insert(int index, object item)

            {

                ((IList<object>)_list).Insert(index, item);

            }

​

            public bool Remove(object item)

            {

                return ((IList<object>)_list).Remove(item);

            }

​

            public void RemoveAt(int index)

            {

                ((IList<object>)_list).RemoveAt(index);

            }

            #endregion IList

​

        }

}