using System;

using System.Collections.Generic;

​

namespace ConsoleApp1

{   

    public class MyClass{

        public readonly int num;

        public static MyClass Factory<T>(List<T> list){

            return new MyClass(list.Count);

        }

        private MyClass(int p_num){

            num=p_num;

        }

    }

    public class Program

    {

        public static void Main()

        {

            var instance = MyClass.Factory(new List<int>{1,3,5});

            var p = instance.num;

            Console.WriteLine(p);

        }

    }

}

​