using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

    }

    public class DummyClassFactory

    {

        public Object GetDummyClassInstance()

        { 

            var dummyClass = new DummyClass();

            switch (DateTime.Now.DayOfWeek)

            {

                // Starting on monday.

                case DayOfWeek.Monday:

                    return (IDisposable)dummyClass;

                case DayOfWeek.Thursday:

                    return (IServiceProvider)dummyClass;

                case DayOfWeek.Friday:

                    return (IEquatable<List<Single>>)dummyClass;

                case DayOfWeek.Saturday:

                    return (IFormattable)dummyClass;

            }

            // return (DummyClassFactory)dummyClass; 

            return dummyClass;

        }

    }

​

    public class DummyClass { }

    public interface IDummyClass { }

}