using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

namespace ConsoleApp11

{

    public class Program

    {

        static IEnumerable<int> CountUp()

        {

            yield return 0;

            yield return 1;

            yield return 2;

        }

​

        static IEnumerable<int> NumberRange(int max)

        {

            for (int i = 0; i < max; i++)

                yield return i;

        }

​

        static IEnumerable<int> InfiniteNumbers()

        {

            int i = 0;

            while (true)

                yield return i++;

        }

​

        public static void Main(string[] args)

        {

            CountUp().Take(2).Dump();

​

            var numbers = NumberRange(20);

            numbers.Dump();

​

            var moreNumbers = InfiniteNumbers().Where(x => x % 2 == 0);

            moreNumbers.Take(100).Dump();

        }

    }

​

    static class MyExt

    {

        public static void Dump<T>(this IEnumerable<T> list)

        {

            Console.Write("(");

            foreach (T e in list)

                Console.Write($"{e}, ");

            Console.WriteLine(")");

        }

    }

}

​