XLColumn

XLColumn.cs

using System;
using System.Text;

public class XLColumn : IEquatable<XLColumn>
{
    private const string mask = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private readonly int columnIndex;

    public XLColumn(int value) {
        columnIndex = value;
    }

    public XLColumn(string value) {
        columnIndex = GetInteger(value);
    }

    public override bool Equals(object obj) {
        var other = obj as XLColumn;
        if (other == null) {
            return Equals(other);
        }
        return false;
    }

    public bool Equals(XLColumn other) => Equals(this, other);

    public override int GetHashCode() => columnIndex;

    public override string ToString() => GetString(columnIndex);

    public static bool Equals(XLColumn a, XLColumn b) {
        // Boxing to prevent infinite loops with implicit conversion
        object oa = a;
        object ob = b;
        if (ReferenceEquals(oa, ob)) {
            return true;
        }
        if (oa == null || ob == null) {
            return false;
        }
        return a.columnIndex == b.columnIndex;
    }

    public static bool operator ==(XLColumn a, XLColumn b) => Equals(a, b);

    public static bool operator !=(XLColumn a, XLColumn b) => !Equals(a, b);

    public static int operator +(XLColumn a, XLColumn b) => a.columnIndex + b.columnIndex;

    public static int operator -(XLColumn a, XLColumn b) => a.columnIndex - b.columnIndex;

    private static int GetInteger(string str) {
        if (str == null) {
            return 0;
        }
        int baseValue = 1;
        int intValue = 0;
        for (int i = str.Length - 1; i >= 0; i--) {
            char c = str[i];
            int index = mask.IndexOf(c);
            if (index == -1) {
                throw new ArgumentOutOfRangeException();
            }
            intValue += (index + 1) * baseValue;
            baseValue *= mask.Length;
        }
        return intValue;
    }

    private static string GetString(int value) {
        if (value < 0) {
            throw new ArgumentOutOfRangeException();
        }
        int baseValue = mask.Length;
        var sb = new StringBuilder();
        while (value > 0) {
            int tmp = (value - 1) / baseValue;
            int index = value - tmp * baseValue;
            char c = mask[index - 1];
            sb.Insert(0, c);
            value = tmp;
        }
        return sb.ToString();
    }

}