/// <summary>
/// Returns a sequence consisting of the head elements and the given tail element.
/// </summary>
/// <typeparam name="T">Type of sequence</typeparam>
/// <param name="head">All elements of the head. Must not be null.</param>
/// <param name="tail">Tail element of the new sequence.</param>
/// <returns>A sequence consisting of the head elements and the given tail element.</returns>
/// <remarks>This operator uses deferred execution and streams its results.</remarks>
public static IEnumerable <T> Append <T>(this IEnumerable <T> head, T tail)
{
if (head == null)
{
throw new ArgumentNullException(nameof(head));
}
return(head is PendNode <T> node
? node.Concat(tail)
: PendNode <T> .WithSource(head).Concat(tail));
}
/// <summary>
/// Prepends a single value to a sequence.
/// </summary>
/// <typeparam name="TSource">The type of the elements of <paramref name="source"/>.</typeparam>
/// <param name="source">The sequence to prepend to.</param>
/// <param name="value">The value to prepend.</param>
/// <returns>
/// Returns a sequence where a value is prepended to it.
/// </returns>
/// <remarks>
/// This operator uses deferred execution and streams its results.
/// </remarks>
/// <code><![CDATA[
/// int[] numbers = { 1, 2, 3 };
/// var result = numbers.Prepend(0);
/// ]]></code>
/// The <c>result</c> variable, when iterated over, will yield
/// 0, 1, 2 and 3, in turn.
public static IEnumerable <TSource> Prepend <TSource>(this IEnumerable <TSource> source, TSource value)
{
if (source == null)
{
throw new ArgumentNullException(nameof(source));
}
return(source is PendNode <TSource> node
? node.Prepend(value)
: PendNode <TSource> .WithSource(source).Prepend(value));
}
public Item(T item, bool isPrepend, PendNode <T> next)
{
if (next == null)
{
throw new ArgumentNullException(nameof(next));
}
Value = item;
IsPrepend = isPrepend;
ConcatCount = next is Item nextItem
? nextItem.ConcatCount + (isPrepend ? 0 : 1)
: 1;
Next = next;
}