Untitled

using System;

namespace test
{
    public class Factory<T>
        where T : Factory<T>, new()
    {
        public virtual T Make()
        {
            return new T();
        }
    }

    public class DerivedA : Factory<DerivedA>
    {
        public DerivedA() { Console.WriteLine("DerivedA ctor"); }
    }

    public class DerivedB : Factory<DerivedB>
    {
        public DerivedB() { Console.WriteLine("DerivedB ctor"); }
    }

    static class main
    {
        static void Main(string[] args)
        {
            DerivedA a = new DerivedA();
            DerivedB b = new DerivedB();

            DerivedB binst = b.Make();
            DerivedA ainst = a.Make();
        }
    }
}