C# In() method

FrameworkExtensions.cs

/// <summary>
/// Checks to see if source is in the items collection.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="source"></param>
/// <param name="items"></param>
/// <returns></returns>
public static bool In<T>(this T source, params T[] items)
{
    if (items == null)
    {
        throw new ArgumentNullException("items");
    }

    return items.Contains(source);
}

/// <summary>
/// Checks to see if source is in the items collection.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="source"></param>
/// <param name="items"></param>
/// <returns></returns>
public static bool In<T>(this T source, IEnumerable<T> items)
{
    if (items == null)
    {
        throw new ArgumentNullException("items");
    }

    return items.Contains(source);
}