using System;

using System.Collections;

using System.Collections.Generic;                   

​

public class Program

{

    public static void Main()

    {

        var owners = new[] { "Karen", "Bob", "John", "Anne" };

        var pets = new[] { "Dog", "Cat", "Bird", "Fish" };

        foreach (var index in 1..3)

        {

            Console.WriteLine($"  {owners[index],-8}{pets[index]}");

        }

​

        Console.WriteLine();

​

        for (int index = 1; index < 3; index++)

        {

            Console.WriteLine($"  {owners[index],-8}{pets[index]}");

        }

​

        Console.WriteLine();

​

        Range range = new(1, 3);

​

        foreach (var index in range)

        {

            Console.WriteLine($"  {owners[index],-8}{pets[index]}");

        }       

    }

}

​

public static class RangeExtensions

{

    /// <summary>

    /// Returns an enumerator that iterates through a <seealso cref="Range"/>.

    /// </summary>

    /// <param name="range">Range to iterate e.g. 4..8</param>

    public static RangeEnumerator GetEnumerator(this Range range)

    {

​

        if (range.Start.IsFromEnd || range.End.IsFromEnd)

        {

            throw new ArgumentException(nameof(range));

        }

​

        return new RangeEnumerator(range.Start.Value, range.End.Value);

​

    }

​

    public struct RangeEnumerator : IEnumerator<int>

    {

        private readonly int _end;

        private int _current;

​

        public RangeEnumerator(int start, int end)

        {

            _current = start - 1;

            _end = end;

        }

​

        public int Current => _current;

        object IEnumerator.Current => Current;

​

        public bool MoveNext() => ++_current < _end;

​

        public void Dispose() { }

        public void Reset()

        {

            throw new NotImplementedException();

        }

    }

}