static void Main(string[] args)
        {
#if iterator
            var calendar = new Calendar();
            var cal      = calendar.Get();
            //var weeks = calendar.GetWeeks();
            Console.WriteLine(cal);

            foreach (var month in cal)
            {
                foreach (var week in month.Weeks)
                {
                    foreach (var date in week.DateTimes)
                    {
                        Console.WriteLine(date.ToString());
                    }
                }
            }
#elif contaractS
            var user = new RegisteredUser();
            user.DoSomthing(1);
#elif generics
            new GenericsSample().Exec();
#elif async
            new AsyncFunctions().Main();
            var single = new SampleAsync().GetSingleAsync();
            Console.WriteLine(single.Result);
            var multi = new SampleAsync().GetMultiAsync();
            Console.WriteLine(multi.Result);
#elif gettersetter
            //var people = new People();
            //people.FirstName = "Taro";
            //people.LastName = "Tanaka";
            //Console.WriteLine(people.FullName);
#elif construct
            var people = new People(age: 5, birthday: DateTime.Now)
            {
                FirstName = "Taro",
                LastName  = "Tanaka"
            };

            var child = new Child1("test", 1);
            Console.WriteLine(child.GetContent());
#elif linq
            new LinqSample().DoSomething();
#endif
        }