public static TSource ElementAt <TSource>(this IEnumerable <TSource> source, int index)
{
if (source == null)
{
throw Error.ArgumentNull("source");
}
IPartition <TSource> partition = source as IPartition <TSource>;
if (partition != null)
{
return(partition.ElementAt(index));
}
IList <TSource> list = source as IList <TSource>;
if (list != null)
{
return(list[index]);
}
if (index >= 0)
{
using (IEnumerator <TSource> e = source.GetEnumerator())
{
while (e.MoveNext())
{
if (index == 0)
{
return(e.Current);
}
index--;
}
}
}
throw Error.ArgumentOutOfRange("index");
}