/// <summary>
/// Returns the only element of a sequence, or a default value if the
/// sequence is empty; this method throws an exception if there is more
/// than one element in the sequence.
/// </summary>
/// <typeparam name="T">
/// The type of the elements of <paramref name="source"/>.</typeparam>
/// <param name="source">The input sequence.</param>
/// <returns>
/// The single element of the input sequence, or default value of type
/// <typeparamref name="T"/> if the sequence contains no elements.
/// </returns>
public static T SingleOrDefault <T>(this IExtremaEnumerable <T> source)
{
if (source == null)
{
throw new ArgumentNullException(nameof(source));
}
return(source.Take(2).AsEnumerable().SingleOrDefault());
}
/// <summary>
/// Returns the first element of a sequence.
/// </summary>
/// <typeparam name="T">
/// The type of the elements of <paramref name="source"/>.</typeparam>
/// <param name="source">The input sequence.</param>
/// <exception cref="InvalidOperationException">
/// The input sequence is empty.</exception>
/// <returns>
/// The first element of the input sequence.
/// </returns>
public static T First <T>(this IExtremaEnumerable <T> source)
{
if (source == null)
{
throw new ArgumentNullException(nameof(source));
}
return(source.Take(1).AsEnumerable().First());
}