public static IEnumerable <EnumeratedItem <T> > WithDescriptions <T>(this IEnumerable <T> items)
{
// To avoid evaluating the whole collection up-front (which may be undesirable, for example
// if the collection contains infinitely many members), read-ahead just one item at a time.
// Get the first item
var enumerator = items.GetEnumerator();
if (!enumerator.MoveNext())
{
yield break;
}
T currentItem = enumerator.Current;
int index = 0;
while (true)
{
// Read ahead so we know whether we're at the end or not
bool isLast = !enumerator.MoveNext();
// Describe and yield the current item
EnumeratedItemDescription description = (index % 2 == 0 ? EnumeratedItemDescription.Odd : EnumeratedItemDescription.Even);
if (index == 0)
{
description |= EnumeratedItemDescription.First;
}
if (isLast)
{
description |= EnumeratedItemDescription.Last;
}
if (index > 0 && !isLast)
{
description |= EnumeratedItemDescription.Interior;
}
yield return(new EnumeratedItem <T>(index, currentItem, description));
// Terminate or continue
if (isLast)
{
yield break;
}
index++;
currentItem = enumerator.Current;
}
}
public bool Is(EnumeratedItemDescription description)
{
return((Description & description) == description);
}
public EnumeratedItem(int index, T item, EnumeratedItemDescription description)
{
Index = index;
Item = item;
Description = description;
}
