RangeEnumerator.cs

using System;
using System.Linq;
using System.Collections.Generic;
using System.Collections;

/// <summary>
/// Provides iterating in foreach and manipulating via LINQ over elements of range
/// </summary>
public struct RangeEnumerator : IEnumerator<int>
{
    private Range _range;
    private int _current;
    private int _mode; // 0 - not started, 1 - started, 2- finished

    private bool HasMoreElement { get { return (_current != _range.Stop) && ((_current < _range.Stop) ^ (_range.Step < 0)); } }


    internal RangeEnumerator(ref Range range)
    {

        _range = range;
        _mode = 0;
        _current = 0;
    }

    public void Dispose() { }


    public bool MoveNext()
    {
        switch (_mode)
        {
            case 0:
                _mode = 1;
                _current = _range.Start;
                return true;
            case 1:
                _current += _range.Step;
                if (!HasMoreElement)
                {
                    _mode = 2;
                    return false;
                }
                return true;
            default: // 2
                return false;
        }
    }

    public void Reset()
    {
        _mode = 0;
    }

    bool IEnumerator.MoveNext()
    {
        return MoveNext();
    }

    void IEnumerator.Reset()
    {
        Reset();
    }

    void IDisposable.Dispose()
    {
        Dispose();
    }

    object IEnumerator.Current { get { return Current as object; } }

    public int Current
    {
        get
        {
            switch (_mode)
            {
                case 1:
                    return _current;
                case 0:
                    throw new InvalidOperationException("Enumeration has not started. Call MoveNext.");
                default: //2
                    throw new InvalidOperationException("Enumeration already finished.");
            }
        }

    }


}