private static IEnumerable <TSource> ElementsInIterator <TSource>(IEnumerable <TSource> source, Range range)
{
Index start = range.Start;
Index end = range.End;
if (source is IList <TSource> list)
{
int count = list.Count;
if (count == 0 && range.Equals(System.Range.All))
{
yield break;
}
int firstIndex = start.IsFromEnd ? count - start.Value : start.Value;
int lastIndex = (end.IsFromEnd ? count - end.Value : end.Value) - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
if (firstIndex < 0 || lastIndex < 0)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
if (firstIndex >= count || lastIndex >= count)
{
ThrowHelper.ThrowArgumentException(ExceptionArgument.range); // Following the behavior of array with range.
}
for (int currentIndex = firstIndex; currentIndex <= lastIndex; currentIndex++)
{
yield return(list[currentIndex]);
}
yield break;
}
using (IEnumerator <TSource> e = source.GetEnumerator())
{
int currentIndex = -1;
if (start.IsFromEnd)
{
if (!e.MoveNext())
{
const int count = 0;
int firstIndex = count - start.Value;
int lastIndex = (end.IsFromEnd ? count - end.Value : end.Value) - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
else
{
Queue <TSource> queue = new Queue <TSource>();
queue.Enqueue(e.Current);
currentIndex++;
int takeLastCount = start.Value;
while (e.MoveNext())
{
if (queue.Count == takeLastCount)
{
queue.Dequeue();
}
queue.Enqueue(e.Current);
currentIndex++;
}
if (queue.Count < takeLastCount)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
int firstIndex = currentIndex + 1 - takeLastCount;
int lastIndex = end.IsFromEnd ? currentIndex - end.Value : end.Value - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
for (int index = firstIndex; index <= lastIndex; index++)
{
yield return(queue.Dequeue());
}
}
}
else
{
int firstIndex = start.Value;
if (!e.MoveNext())
{
if (range.Equals(System.Range.All))
{
yield break;
}
const int count = 0;
int lastIndex = (end.IsFromEnd ? count - end.Value : end.Value) - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
ThrowHelper.ThrowArgumentException(ExceptionArgument.range); // Following the behavior of array with range.
}
currentIndex++;
while (currentIndex < firstIndex && e.MoveNext())
{
currentIndex++;
}
if (currentIndex != firstIndex)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
if (end.IsFromEnd)
{
int skipLastCount = end.Value;
if (skipLastCount > 0)
{
Queue <TSource> queue = new Queue <TSource>();
do
{
if (queue.Count == skipLastCount)
{
yield return(queue.Dequeue());
}
queue.Enqueue(e.Current);
currentIndex++;
}while (e.MoveNext());
}
else
{
do
{
yield return(e.Current);
currentIndex++;
}while (e.MoveNext());
}
if (firstIndex + skipLastCount > currentIndex)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
}
else
{
int lastIndex = end.Value - 1;
if (lastIndex < firstIndex - 1)
{
ThrowHelper.ThrowOverflowException(); // Following the behavior of array with range.
}
if (lastIndex == firstIndex - 1)
{
yield break;
}
yield return(e.Current);
while (currentIndex < lastIndex && e.MoveNext())
{
currentIndex++;
yield return(e.Current);
}
if (currentIndex != lastIndex)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.range); // Following the behavior of array with range.
}
}
}
}
}